Federal Motor Vehicle Safety Standards; Minimum Sound Requirements for Hybrid and Electric Vehicles
Notice Of Proposed Rulemaking (Nprm).
As required by the Pedestrian Safety Enhancement Act (PSEA) of 2010 this rule proposes to establish a Federal motor vehicle safety standard (FMVSS) setting minimum sound requirements for hybrid and electric vehicles. This new standard would require hybrid and electric passenger cars, light trucks and vans (LTVs), medium and heavy duty, trucks, and buses, low speed vehicles (LSVs), and motorcycles to produce sounds meeting the requirements of this standard. This proposed standard applies to electric vehicles (EVs) and to those hybrid vehicles (HVs) that are capable of propulsion in any forward or reverse gear without the vehicle's internal combustion engine (ICE) operating. This standard would ensure that blind, visually-impaired, and other pedestrians are able to detect and recognize nearby hybrid and electric vehicles, as required by the PSEA, by requiring that hybrid and electric vehicles emit sound that pedestrians would be able to hear in a range of ambient environments and contain acoustic signal content that pedestrians will recognize as being emitted from a vehicle.
The benefit of reducing the pedestrian injury rate per registered vehicle of HVs to ICE vehicles when 4.1% of the fleet is HV and EV would be 2790 fewer pedestrian and pedalcyclist injuries. We also estimate that this proposal will result in 10 fewer pedestrian and pedalcyclist injuries caused by LSVs. Thus, 2800 total injured pedestrians are expected to be avoided due to this proposal representing 35 equivalent lives saved. We do not estimate any quantifiable benefits for EVs because it is our view that EV manufacturers would have installed alert sounds in their cars without passage of the PSEA and this proposed rule. Comparison of costs and benefits expected due to this rule provides a cost of $0.83 to $0.99 million per equivalent life saved across the 3 and 7 percent discount levels for the light EV and HV and LSV fleet. According to our present model, a countermeasure that allows a vehicle to meet the proposed minimum sound requirements would be cost effective compared to our comprehensive cost estimate of the value of a statistical life of $6.3 million.
1 action from January 2013
Table of Contents Back to Top
- FOR FURTHER INFORMATION CONTACT:
- SUPPLEMENTARY INFORMATION:
- Table of Contents
- I. Executive Summary
- II. Background
- III. Pedestrian Safety Enhancement Act of 2010
- IV. Consultation With External Organizations
- V. Safety Problem
- A. Comparing the Vehicle to Pedestrian Crash Experience of ICE Vehicles and HVs and EVs
- Crash Risk
- B. Need for Independent Mobility of People Who Are Visually Impaired
- Example 1:
- Example 2:
- Example 3:
- VI. NHTSA Research and Industry Practices
- A. NHTSA Phase 1 Research 
- Safety Scenarios for Pedestrians Who Are Blind or Visually-Impaired
- Auditory Detectability of Vehicles in Critical Safety Scenarios 
- B. NHTSA Phase 2 Research
- Recordings of Actual ICE Sounds
- Synthesized ICE-Equivalent Sounds
- Alternative, Non-ICE-Like Sounds Designed for Detectability
- Hybrid of Options Discussed Above
- Human Subject Evaluation of Detectability
- C. NHTSA Phase 3 Research
- VRTC Acoustic Measurements
- Test Scenarios 
- Interpretation of Results
- Acoustic Analysis Performed by Volpe
- Background Noise
- Critical Frequency Range
- Loudness Models
- D. International Approach to Pedestrian Alert Sounds
- E. SAE Sound Measurement Procedure
- F. Alert Sounds Currently Provided by Manufacturers
- G. The Notice of Intent To Prepare an Environmental Assessment
- Comments Received in Response to NOI
- VII. NHTSA's Proposal
- A. Acoustic Specifications Developed To Enhance Detection and Recognition
- B. Critical Operating Scenarios
- 1. Stationary But Activated
- 2. Reverse
- 3. Acceleration and Deceleration
- 4. Constant Speed
- C. Application
- 1. The Definition of Hybrid Vehicle
- 2. Vehicles With a GVWR Over 10,000 Pounds
- 3. Electric Motorcycles
- 4. Low-Speed Vehicles
- 5. Quiet ICE Vehicles
- D. Requirements
- 1. Acoustic Parameters Designed According to a Detectability Model
- 2. Recognizability Requirements
- 3. Prohibition Against Modifying a Vehicle's Sound
- 4. Phase-in Schedule
- E. Compliance Test Procedure
- 1. Test Condition
- 2. Vehicle Condition
- 3. Test Procedure
- a. Start-Up
- b. Stationary But Activated and Directivity
- c. Reverse
- d. Constant Speed Tests
- e. Pitch Shifting
- f. Recognizability
- g. Vehicles of the Same Make and Model Emitting the Same Sound
- VIII. Alternatives Considered But Not Proposed
- A. Requiring Vehicle Sound To Be Playback of an ICE Recording
- B. Requiring That the Alert Sound Adapt to the Ambient
- C. Acoustic Profile Designed Around Sounds Produced by ICE Vehicles
- D. Acoustic Profiles Suggested by Manufacturers
- E. International Guidelines for Vehicle Alert Sounds
- F. Suggestions in Comments to the NOI That Did Not Satisfy the Statement of Purpose and Need for the Rulemaking
- G. Possible Jury Testing for Recognizability of a Synthetic Sound
- IX. NHTSA's Role in the Development of a Global Technical Regulation
- X. Analysis of Costs, Benefits, and Environmental Effects
- A. Benefits
- B. Costs
- C. Comparison of Costs and Benefits
- D. Environmental Effects
- XI. Regulatory Notices and Analyses
- Executive Order (E.O.) 12866 (Regulatory Planning and Review), E.O. 13563, and DOT Regulatory Policies and Procedures
- Executive Order 13609: Promoting International Regulatory Cooperation
- National Environmental Policy Act
- Regulatory Flexibility Act
- Executive Order 13132 (Federalism)
- Executive Order 12988 (Civil Justice Reform)
- Unfunded Mandates Reform Act
- Paperwork Reduction Act
- Summary of the Collection of Information
- Description of the Need for the Information and Use of the Information
- Description of the Likely Respondents (Including Estimated Number, and Proposed Frequency of Response to the Collection of Information)
- Estimate of the Total Annual Reporting and Recordkeeping Burden Resulting From the Collection of Information
- Executive Order 13045
- National Technology Transfer and Advancement Act
- Executive Order 13211
- Regulation Identifier Number (RIN)
- Plain Language
- Privacy Act
- Public Participation
- How do I prepare and submit comments?
- How can I be sure that my comments were received?
- How do I submit acoustic recordings?
- How do I submit confidential business information?
- Will the agency consider late comments?
- How can I read the comments submitted by other people?
- List of Subjects
- Proposed Regulatory Text
- PART 571—FEDERAL MOTOR VEHICLE SAFETY STANDARDS
- PART 585—PHASE-IN REPORTING REQUIREMENTS
- Subpart N— Minimum Sound Requirements for Hybrid and Electric Vehicles Reporting Requirements
- Subpart N—Minimum Sound Requirements for Hybrid and Electric Vehicles Reporting Requirements
- Appendix A—Glossary of Sound Engineering Terms
- Appendix B. Acoustic Primer
- What is sound?
- How is sound perceived?
- How is sound quantified?
Tables Back to Top
- Discounted Benefits for Passenger Cars (PCs) and LTVs, MY2016, 2010$
- Total Costs for PCs and LTVs, MY2016, 2010$
- Costs and Scaled Benefits for LSVs, MY20163
- Total Benefits and Costs Summary for Light Vehicles and Low Speed Vehicles, MY2016, 2010$
- Table 1—Overall A-Weighted Sound Level at the Microphone Location (12 ft)
- Table 2—Time-to-Vehicle Arrival and Detection Distance for 6 mph Vehicle Pass-by by Vehicle Type and Ambient Condition
- Table 3—Time-to-Vehicle Arrival and Detection Distance for Vehicle Backing Out by Vehicle and Ambient Condition
- Table 4—Time-to-Vehicle Arrival and Detection Distance for Vehicle Decelerating From 20 to 10 mph by Vehicle Type and Ambient Condition
- Table 5—Average Time-to-Vehicle Arrival by Scenario, Vehicle Type and Ambient Sound
- Table 6—Minimum Overall A-weighted Level (LAeq, 1/2; sec)by Vehicle Operation
- Table 7—A-weighted One-Third-Octave-Band Spectra at Microphone Line LAeq, 1/2 sec
- Table 8—Mean Detection Distance (ft) for All Sounds at Two Amplitudes and for the Reference ICE Vehicle
- Table 9—Pass-By Sound Level for HEV/EV Vehicles Without Alert Sound Active Versus Counterpart ICE Vehicles
- Table 10—Preliminary Results of Motorcycle Crashes
- Table 11—Computation of Adjustment of SPL (A-Weighted dB) From Source to SAE Microphone Location
- Table 12—Minimum Sound Levels for Detection
- Table 13—Minimum A-Weighted Sound Levels Based on ICE Mean Levels
- Table 14—Minimum A-Weighted Sound Levels Based on ICE Mean Levels Minus One Standard Deviation
- Table 15—Quiet Cars Target Population Injuries Reported (GES, NiTS) and Unreported Pedestrians and Pedalcyclists, by Vehicle
- Table 16—Enhanced Injury Rate (EIR) for Pedestrians for 2016 Model Year122
- Enhanced Injury Rate (EIR) for Pedestrians for 2016 Model Year123
- Table 17—Estimated/Predicted Hybrid and Electric Vehicle Sales Proposed To Be Required To Provide an Alert Sound
- Table 18—Total Costs
- Table 19—Discounted Benefits MY 2016, 2010$
- Table 20—Total Costs 2010$
- Table 21—Net Impacts 2010$
- Table 22—Costs and Scaled Benefits for LSVs, MY2016126
- Table 1—One-Third Octave Band Min. SPL Requirements for Sound When Stationary But Activated
- Table 2—One-Third Octave Band Min. SPL Requirements for Sound while Backing
- Table 3—One-Third Octave Band Min. SPL Requirements for 10 km/h Pass-by
- Table 4—One-Third Octave Band Min. SPL Requirements for 20 km/h Pass-by
- Table 5—One-Third Octave Band Min. SPL Requirements for 30 km/h Pass-by
- Table 6—Corrections for Background Noise
- Table 8—Example of One-Third-Octave Data in Tabular Form: Summary of Ambient Levels during ICE Measurements, A-weighted Level, dB(A)
DATES: Back to Top
Comments must be received on or before March 15, 2013.
ADDRESSES: Back to Top
You may submit comments to the docket number identified in the heading of this document by any of the following methods:
- Federal eRulemaking Portal: go to http://www.regulations.gov. Follow the online instructions for submitting comments.
- Mail: Docket Management Facility, M-30, U.S. Department of Transportation, West Building, Ground Floor, Rm. W12-140, 1200 New Jersey Avenue SE., Washington, DC 20590.
- Hand Delivery or Courier: West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE., between 9 a.m. and 5 p.m. Eastern Time, Monday through Friday, except Federal holidays.
- Fax: (202) 493-2251.
Regardless of how you submit your comments, you should mention the docket number of this document.
You may call the Docket at 202-366-9324.
Instructions: For detailed instructions on submitting comments and additional information on the rulemaking process, see the Public Participation heading of the Supplementary Information section of this document. Note that all comments received will be posted without change to http://www.regulations.gov, including any personal information provided.
Privacy Act: Please see the Privacy Act heading under Rulemaking Analyses and Notices.
FOR FURTHER INFORMATION CONTACT: Back to Top
For non-legal issues, Ms. Gayle Dalrymple, Office of Crash Avoidance Standards (telephone: 202-366- 5559) (fax: 202-493-2990). Ms. Dalrymple's mailing address is National Highway Traffic Safety Administration, NVS-112, 1200 New Jersey Avenue SE., Washington, DC 20590.
For legal issues, Mr. Thomas Healy, Office of the Chief Counsel (telephone: 202-366-2992) (fax: 202-366-3820). Mr. Healy's mailing address is National Highway Traffic Safety Administration, NCC-112, 1200 New Jersey Avenue SE., Washington, DC 20590.
SUPPLEMENTARY INFORMATION: Back to Top
Table of Contents Back to Top
I. Executive Summary
III. Pedestrian Safety Enhancement Act of 2010
IV. Consultation With External Organizations
V. Safety Problem
A. Comparing the Vehicle to Pedestrian Crash Experience of Internal Combustion Engine Vehicles to Hybrid and Electric Vehicles
B. Need for Independent Mobility of People Who Are Visually Impaired and Blind
VI. NHTSA Research and Industry Practices
A. NHTSA Phase 1 Research
B. NHTSA Phase 2 Research
C. NHTSA Phase 3 Research
D. International Approach to Pedestrian Alert Sounds
E. SAE Sound Measurement Procedure
F. Alert Sounds Currently Provided by Manufacturers
G. The Notice of Intent To Prepare an Environmental Assessment
VII. NHTSA's Proposal
A. Acoustic Specifications Developed To Enhance Detection and Recognition
B. Critical Operating Scenarios
1. Stationary But Activated
3. Acceleration and Deceleration
4. Constant Speed
1. The Definition of Hybrid Vehicle
2. Vehicles With a GVWR Over 10,000 lbs
3. Electric Motorcycles
4. Low Speed Vehicles
5. Quiet Internal Combustion Engine Vehicles
1. Acoustic Parameters Designed According to a Detectability Model
2. Recognizability Requirements
3. Prohibition Against Modifying a Vehicle Sound
4. Phase-in Schedule
E. Compliance Test Procedure
1. Test Condition
2. Vehicle Condition
3. Test Procedure
b. Stationary But Activated and Directivity
d. Constant Speed
e. Pitch Shifting
g. Vehicles of the Same Make and Model Emitting the Same Sound
VIII. Alternatives Considered But Not Proposed
A. Requiring Vehicle Sound To Be Playback of an Internal Combustion Engine Recording
B. Requiring That the Alert Sound Adapt to the Ambient
C. Acoustic Profile Designed Around Sounds Produces by Internal Combustion Engine Vehicles
D. Acoustic Profiles Suggested by Manufacturers
E. International Guidelines for Vehicle Alert Sounds
F. Suggestions in Comments to the Notice of Intent That Did Not Satisfy the Statement of Purpose and Need for the Rulemaking
G. Possible Jury Testing for Recognition of a Synthetic Sound
IX. NHTSA's Role in the Development of a Global Technical Regulation
X. Analysis of Costs, Benefits and Environmental Effects
C. Comparison of Costs and Benefit
D. Environmental Effects
XI. Regulatory Notices and Analyses
I. Executive Summary Back to Top
As required by the PSEA,  this rule proposes to establish FMVSS No.141, Minimum Sound Requirements for Hybrid and Electric Vehicles, which would require hybrid and electric passenger cars, LTVs, medium and heavy duty trucks and buses, LSVs, and motorcycles to produce sounds meeting the requirements of this standard. This proposed standard applies to EVs and to those HVs that are capable of propulsion in any forward or reverse gear without the vehicle's ICE operating. The PSEA requires NHTSA to establish performance requirements for an alert sound that is recognizable as motor vehicle in operation that allows blind and other pedestrians to reasonably detect a nearby EV or HV operating below the crossover speed. The crossover speed is the speed at which tire noise, wind noise, and other factors eliminate the need for a separate alert sound. The PSEA defines “alert sound” as “a vehicle-emitted sound to enable pedestrians to discern vehicle presence, direction, location and operation.”  The legal authority for this rulemaking comes from the PSEA and 49 U.S.C. 30111.
This standard will ensure that blind, visually-impaired, and other pedestrians are able to detect and recognize nearby hybrid and electric vehicles by requiring that hybrid and electric vehicles emit sound that pedestrians will be able to hear in a range of ambient environments and contain acoustic signal content that pedestrians will recognize as being emitted from a vehicle. The proposed standard establishes minimum sound requirements for hybrid and electric vehicles when operating under 30 kilometers per hour (km/h) (18 mph), when the vehicle's starting system is activated but the vehicle is stationary, and when the vehicle is operating in reverse.
The requirements of this proposal apply only to those HVs that are capable of propulsion in any forward or reverse gear without the vehicle's ICE operating because these were the vehicles that the agency believes fall under the definition of “hybrid vehicle” contained in the PSEA. The agency chose a crossover speed of 30 km/h because this was the speed at which the sound levels of the hybrid and electric vehicles measured by the agency approximated the sound levels produced by similar ICE vehicles. This proposal contains minimum sound requirements for the activated but stationary operating condition because the definition of alert sound in the PSEA, as explained in Section III of this NPRM, requires the agency to issue minimum sound requirements to allow pedestrians to detect hybrid and electric vehicles. We have tentatively determined that this requirement can be best met by requiring vehicles to emit sound in this operating condition.
At lower speeds, hybrid and electric vehicles produce less sound than vehicles propelled by an ICE. At higher speeds, tire and wind noise are the main contributors to vehicles noise output so at higher speeds the sounds produced by hybrid and electric vehicles and ICE vehicles are similar. Because hybrid and electric vehicles do not produce as much sound as ICE vehicles when operating at lower speeds, pedestrians and other road users may not be aware of the presence of a nearby hybrid or electric vehicle. If a hybrid vehicle is involved in a low speed maneuver (defined as making a turn, slowing or stopping, backing up, entering or leaving a parking space, or starting in traffic), it is 1.38 times more likely than an ICE vehicle to be involved in a collision with a pedestrian and 1.33 times more likely to be involved in a collision with a pedalcyclist. We believe that this difference in accident rates is mostly attributable to the pedestrians' inability to detect these vehicles by hearing them during these maneuvers. We seek comment on this assumption.
Statistics for pedestrian collision rates of hybrid and electric vehicles with a GVWR over 4,536 kg (10,000 lb), and motorcycles were not available because of the limited penetration of these vehicles into the fleet. NHTSA expects that should the penetration of hybrid and electric heavy vehicles, and motorcycles reach the current rate of penetration of light hybrid and electric vehicles into the fleet, then the difference in pedestrian collision rates between hybrid and electric heavy vehicles, and motorcycles and their traditional ICE counterparts will be similar to the difference in pedestrian collision rates between light HVs and light ICE vehicles.
In addition to analyzing crash data, the agency measured the sound produced by HVs, EVs and ICE vehicles to determine the difference in sound output between the propulsion types at different speeds and conducted research to see if there was a difference in the ability of pedestrians to detect approaching hybrid and electric vehicles versus ICE vehicles. The agency also used acoustic models to determine the frequency composition of sounds that would give pedestrians the best chance to detect approaching hybrid and electric vehicles without contributing undesirably to surrounding ambient noise levels.
The proposed standard ensures that pedestrians will be able to determine whether a hybrid or electric vehicle is accelerating or decelerating by requiring the frequency content of the sound emitted by the vehicle to increase in a manner that is similar to the sound produced by ICE vehicles when accelerating and decelerating. The agency developed the minimum sound specifications contained in this proposal using a detection model that estimated the distance at which a pedestrian would be able hear a given sound in the presence of a given ambient sound profile. The standard also requires, as mandated by the PSEA, that all vehicles of the same make, model and model year emit the same sound.
The PSEA requires that the final rule establishing this standard be issued by January 4, 2014 and include a phase-in schedule that concludes with “full compliance with the required motor vehicle safety standard for motor vehicles manufactured on or after September 1st of the calendar year that begins 3 years after the date on which the final rule is issued.” For example the means that if the final rule is issued January 4, 2014, compliance would commence on September 1, 2015, which would mark the start of a three-year phase-in period. We tentatively conclude that the following phase in schedule is reasonable for manufacturers and allows the fastest implementation of the standard for pedestrian safety:
30 percent of the subject vehicles produced on or after September 1of the first year of the phase in;
60 percent of the subject vehicles produced on or after September 1of the second year of the phase in;
90 of the subject vehicles produced on or after September 1of the third year of the phase in; and
100 percent of all vehicles produced on or after, by September 1 of the year that begins three years after the date that the final rule is issued.
As discussed in detail in Section X of this notice, the benefits of this proposed rule, if made final, will accrue from injuries to pedestrians that will be avoided, assuming that the rule will cause the pedestrian injury rate for HVs and EVs to decrease to that of ICE vehicles. As discussed in Section V, a traditional analysis of pedestrian fatalities is not appropriate for this rulemaking. If HVs and EVs continue to rise in popularity and increase their role in the U.S. fleet to four percent of all vehicle registrations, unchanged by rulemaking or industry action, a total of 2,790 injured pedestrians and pedalcyclists would be expected over the life time of the 2016 model year fleet due to the pedestrians' and pedalcyclists' inability to detect these vehicles by hearing. We estimate that the benefit then of reducing the pedestrian injury rate per registered vehicle of HVs to ICE vehicles when four percent of the fleet is HV and EV would be 2,790 fewer injured pedestrians and pedalcyclists. We do not estimate any quantifiable benefits in pedestrian or pedalcyclist injury reduction for EVs because it is our view that EV manufacturers would have installed alert sounds in their cars without passage of the PSEA and this proposed rule. We also estimate that this proposal will result in 10 fewer injured pedestrians and pedalcyclists caused byLSVs.
|3%discount||Pedestrians||Pedalcyclists||Total PED + CYC|
|3% discount factor||Total monetized benefits||Total ELS||3% discount factor||Total monetized benefits||Total ELS||3% discount factor||Total monetized benefits||Total ELS|
|7%discount||Pedestrians||Pedalcyclists||Total PED + CYC|
|7% discount factor||Total monetized benefits||Total ELS||7% discount factor||Total monetized benefits||Total ELS||7% discount factor||Total monetized benefits||Total ELS|
|3%discount||Sales||Sales impacted||Fuel costs/veh||Fuel costs (total)||Install costs/veh||Install costs total||Total cost/veh||Total costs|
|7%discount||Sales||Sales impacted||Fuel costs/veh||Fuel costs (total)||Install costs/veh||Install costs total||Total cost/veh||Total costs|
|Discount rate||Sales ratio LSV to light vehicle||Sales||Scaled costs||Scaled injuries (undisc.)||Scaled ELS||Scaled benefits||Scaled benefits minus scaled costs|
NHTSA estimates the fuel and installation cost of adding a speaker system in order to comply with the requirements of this proposal to be around $35 per vehicle for light vehicles. We estimate the total fuel and installation costs of this proposal to the light EV, HV and LSV fleet to be $23.6M at the 3 percent discount rate and $22.9M at the 7 percent discount rate. The estimated total installation cost for hybrid and electric heavy and medium duty trucks and buses and electric motorcycles is $1.48M for MY 2016. We have only calculated the benefits of this proposal for light EVs, HVs and LSVs because we do not have crash rates for hybrid and electric heavy and medium duty trucks and buses and electric motorcycles. To estimate the benefits of this proposal we have converted injured pedestrians and pedalcyclists avoided into equivalent lives saved. We estimate that the impact of this proposal in pedestrian and pedalcyclist injury reduction in light vehicles and LSVs will be 28.15 equivalent lives saved at the 3 percent discount rate and 23.06 equivalent lives saved at the 7 percent discount rate. The benefits of this proposal for the light EV and HV and LSV fleet are $178.7M at the 3 percent discount rate and $146.3M at the 7 percent discount rate. Comparison of costs and benefits expected due to this proposal for the light EV, HV and LSV fleet provides a cost of $0.83 to $0.99 million per equivalent life saved across the 3 and 7 percent discount levels. According to our present model, a countermeasure that allows a vehicle to meet the proposed minimum sound requirements would be cost effective compared to our comprehensive cost estimate of the value of a statistical life of $6.3 million.
|3% discount rate||7% discount rate|
|Total Monetized Benefits||$178.7M||$146.3M|
|Total Costs (Install+Fuel)||23.5M||22.9M|
|Total Net Impact (Benefit—Costs)||155.2M||123.4M|
II. Background Back to Top
Whether or not a vehicle can be easily detected by the sound it makes is a product of vehicle type, vehicle speed, and ambient sound level. Quieter vehicles, such as EVs and HVs, can reduce pedestrians' ability to assess the state of nearby traffic and, as a result, can have an impact on pedestrian safety. EVs and HVs may pose a safety problem for pedestrians, in particular pedestrians who are blind or visually impaired and who therefore rely on auditory cues from vehicles to navigate. For these pedestrians, the primary safety issue arises when an HV or EV operates quietly using its electric motor for propulsion at low speeds. This is also the case when other auditory cues, such as the noise from the vehicle's tires and wind resistance, are less noticeable.
Since August 2007, NHTSA has been monitoring the work of the Society of Automotive Engineers' (SAE) Vehicle Sound for Pedestrians (VSP) Committee. Participants in the VSP committee include vehicle manufacturers, suppliers, consulting firms, government, and other interested parties. The VSP committee's primary goal is to develop a test procedure to measure the minimum sound output of a motor vehicle. In September 2011, the SAE published the test procedure, Measurement of Minimum Noise Emitted by Road Vehicles, (SAE-J2889-1).  The purpose of J2889-1 is to provide an objective, technology-neutral test to measure the minimum sound emitted by a vehicle in a specified ambient noise condition. This is a test procedure only and does not describe the VSP committee's rationale, provide recommendations about how sounds for HVs and EVs should be developed or produced, nor does it specify the ambient condition at which a vehicle sound should be detectable for the safety of pedestrians.
On May 30, 2008, NHTSA published a notice  in the Federal Register announcing that the agency would hold a public meeting on June 23, 2008 for government policymakers, stakeholders from organizations representing people who are blind or visually impaired, industry representatives, and public interest groups to discuss the technical, environmental and safety issues associated with EVs, HVs, and quiet ICE vehicles, and the safety of pedestrians. The presentations submitted at the public meeting and a transcript of the meeting can be found in Docket No. NHTSA-2008-0108 on the Web site http://www.regulations.gov.  Topics discussed at the meeting included a statement of the problem, general pedestrian safety, sound measurement and mobility, automotive industry perspective, SAE work and status, potential solutions, and noise abatement. At the conclusion of the public meeting, NHTSA indicated the agency's intention to put together a research plan and encouraged participants to add comments and ideas to the docket. NHTSA issued a research plan to investigate the topic of quieter vehicles and the safety of pedestrians on May 6, 2009. 
In September 2009, NHTSA published a technical report documenting the incidence of crashes involving hybrid-electric passenger vehicles and pedestrians and pedalcyclists.  The analysis included a sample of 8,387 hybrid and 559,703 ICE vehicles. The analysis used data from 12 states and a subset of model-year 2000 and later vehicles. The results of the crash data analysis show that HVs are two times more likely than ICE vehicles to be in a pedestrian crash where the vehicle is backing out, slowing/stopping, starting in traffic, and entering or leaving a parking space/driveway. The vehicles involved in such crashes are likely to be moving at low speeds at which the difference between the sounds emitted by ICE vehicles and HVs is substantial. The crash incidence rate for the combined set of maneuvers is 0.6 percent and 1.2 percent for ICE vehicles and HVs respectively and the difference is statistically significant. Some of the factors considered in this analysis are: (1) vehicle maneuver prior to the crash; (2) speed limit as a proxy for vehicle travel speed; and (3) weather and lighting condition at the time of the crash.
In October 2009, NHTSA issued a report entitled “Research on Quieter Cars and the Safety of Blind Pedestrians, A Report to Congress.”  The report briefly discusses the quieter vehicle safety issue, how NHTSA's research plan would address the issue, and the status of the agency's research in implementing that plan.
In April 2010, NHTSA issued a report presenting results of Phase 1 of the agency's research.  This report documents the overall sound levels and general spectral content for a selection of ICE vehicles and HVs in different operating conditions, evaluates vehicle detectability for two background noise levels, and considers countermeasure concepts that are categorized as vehicle-based, infrastructure-based, and systems requiring vehicle-pedestrian communications.
The results show that the overall sound levels for the HVs tested are noticeably lower at low speeds than for the ICE vehicles tested. Overall, study participants were able to detect any vehicle sooner in the low ambient noise condition. ICE vehicles tested were detected sooner than their HV twins except for the test scenario in which the target vehicle was slowing down. In this scenario, HVs were detected sooner because of the distinctive sound emitted by the regenerative braking system on the HVs. Response time to detect a target vehicle varies by vehicle operating condition, ambient sound level, and vehicle type (i.e., ICE vehicle versus HV in EV mode).
NHTSA initiated additional research (Phase 2) in March 2010 to explore potential audible countermeasures to be used in vehicles while operating in electric mode in specific low speed conditions.  The potential countermeasures explored included quantitative specifications for sound levels and spectral profiles for detectability. The feasibility of objectively specifying other aspects of sound quality for the purpose of predicting recognizability was also explored.
In our Phase 2 study, researchers assumed that acoustic countermeasures should provide alerting information at least equivalent to the cues provided by ICE vehicles. Groups representing people who are blind or visually impaired have expressed a preference for sound(s) that will be recognized as that of an approaching vehicle so that it will be intuitive for all pedestrians.  In the Phase 2 research, acoustic data acquired from a sample of ICE vehicles was used to determine the sound levels at which synthetic vehicle sounds, developed as countermeasures, could be set. ICE equivalent sounds were specified using overall A-weighted sound levels and, one-third octave band spectral content. (See Appendix A, “Glossary of Sound Engineering Terms” and Appendix B, “Acoustic Primer” for definitions and explanations of all acoustic terms used in this notice.)
Psychoacoustic models and human subject testing were used to explore issues of detectability, masking, and recognition of ICE-like and alternative sound countermeasures. Psychoacoustic models showed that frequency components between 1600 and 5000 Hz were more detectable due to strong signal strength and relatively low ambient levels in this range. Also, frequency components below 315 Hz were often masked by urban ambient noise.  Human subject studies were conducted to evaluate countermeasure sounds in a controlled outdoor environment for six miles per hour forward pass-by with the counter measure sound output set at 59.5 A-weighted dB and then at 63.5 A-weighted dB measured 2 meters from the vehicle centerline. The sounds included ICE-like sounds, alternative (non-ICE-like) sounds designed according to psychoacoustic principles to improve detectability, and sounds that combine alternative sounds with some ICE-like components. In addition to the countermeasure sounds, an ICE vehicle sound was included in the study as a baseline for comparison purposes.
The results of this research show that synthetic sounds that resemble those of an ICE produce detection distances similar to actual ICE vehicles. Some of the synthetic sounds examined in the study that were designed according to psychoacoustic principles produced detection distances twice as long as those of ICE sounds. The study participants had difficulty detecting synthetic sounds that contained only the fundamental of the combustion noise of the engine (the lowest frequency associated with the combustion).
This research examined four potential ways in which countermeasure sounds could be specified. The study examined countermeasure sounds based on recordings of ICE vehicles, synthetically generated countermeasure sounds that emulate the sounds of an ICE, non-ICE like countermeasure sounds designed for maximum detectability at a given sound-pressure level, and synthetically generated sounds that have special characteristics to enhance detection and characteristics that ensure that the sounds contain ICE-like components to enhance recognizability. The report noted that an objective specification for non-ICE-like sounds is more difficult to develop than one for synthetic sound generators that emulate the sound of typical ICEs. The report also noted that the former approach could result in a wider variety of sounds, some of which might be not recognized as a vehicle or might be perceived as annoying.
In early 2011, NHTSA initiated additional research and data collection activities to further support this rulemaking (Phase 3). Acoustic measurements and analyses were completed to support the development of specifications for alerting sounds and test procedures for compliance with agency requirements. Acoustic data was gathered from eight vehicles: four ICE vehicles and four EVs/HVs with alerting sounds (one production and three prototype vehicles). The SAE J2889-1 test procedure was used to measure the sound levels for the stopped and pass-by conditions. Acoustic measurements were completed on an ISO 10844:1994 noise pad. All HVs and EVs were measured in electric propulsion mode.
Variations on SAE J2889-1 were used to explore other aspects such as directivity, sound level as a function of vehicle speed, and to capture binaural recordings. Directivity refers to the relative proportions of acoustical energy that is emitted from a source, in this case a vehicle, as a function of direction to the front, back, left, and right. Binaural recordings were captured for potential use in future research activities. Acoustic measurements, modeling, and sound simulation tools were used to identify sound attributes that aid in detection of alert sounds and recognition of these sounds as a motor vehicle.
Two approaches were considered in the development of parameters for alert sounds. In one approach, sound levels for the alert sound were developed using loudness models and a calculation of safe detection distances. In the other approach, sound levels for alert sounds were based on the sound of current ICE vehicles. This research focused on developing specifications that can be applied to all sounds and that are objective and practical.
All of the research activities summarized above are described in more detail in Section VI. NHTSA Research and Industry Practices.
III. Pedestrian Safety Enhancement Act of 2010 Back to Top
On January 4, 2011, the Pedestrian Safety Enhancement Act of 2010 (Public Law 111-373) was signed into law. The Pedestrian Safety Enhancement Act (PSEA) requires NHTSA to conduct a rulemaking to establish a Federal Motor Vehicle Safety Standard (FMVSS)  requiring an “alert sound”  for pedestrians to be emitted by all types of motor vehicles  that are electric vehicles  (EVs) or hybrid vehicles  (HVs). The covered types of vehicles include light vehicles (passenger cars, vans, sport utility vehicles and pickup trucks), as well as LSVs, motorcycles, medium and heavy trucks and buses. Trailers are specifically excluded from the requirements of the PSEA. The PSEA requires NHTSA to establish performance requirements for an alert sound that allows blind and other pedestrians to reasonably detect a nearby EV or HV. The PSEA defines “alert sound” as a vehicle-emitted sound that enables pedestrians to discern the presence, direction,  location, and operation of the vehicle.  Thus, in order for a vehicle to satisfy the requirement in the PSEA to provide an “alert sound,” the sound emitted by the vehicle must satisfy that definition. The alert sound must not require activation by the driver or the pedestrian, and must allow pedestrians to reasonably detect an EV or HV in critical operating scenarios such as constant speed, accelerating, or decelerating. In addition to the operating scenarios previously mentioned the definition of alert sound in the PSEA requires the agency to establish requirements for a sound while the vehicle is activated but stationary and when the vehicle is operating in reverse.
The agency has concluded that the requirement in the PSEA that the alert sound must allow pedestrians to “discern vehicle presence, direction, location, and operation,”  requires the agency to establish minimum sound requirements for the stationary but activated operating condition. The requirement that pedestrians be able to discern vehicle presence must be read along with the requirements that the sound allow pedestrians to discern direction, location, and operation. The term “presence” means something that is in the immediate vicinity. The term “operation” means a state of being functional or operative. Read together the definition of alert sound requires that pedestrians be able to detect vehicle presence when the vehicle is in operation. A vehicle with an engaged ignition is in a state of being functional even though it may not be moving. It is the agency's position that the provision that pedestrians be able to detect the presence of a vehicle that is turned on requires that the vehicle emit a minimum sound level when the vehicle is stationary, but the starting system is activated.
The agency believes that the PSEA requires the agency to establish requirements for a sound while the vehicle is moving reverse for the same reason that a sound while the vehicle is stationary is required. The PSEA requires minimum sound level requirements promulgated by NHTSA to allow pedestrians to discern vehicle presence and operation. A vehicle moving in reverse is unquestionably operating, thus a minimum sound level is required for this condition.
The PSEA also requires that the minimum sound level requirements promulgated by NHTSA allow pedestrians to discern the direction of the vehicle. This language also indicates that the PSEA requires any standard to establish minimum sound requirements for when the vehicle is operating in reverse.
Because the PSEA directs NHTSA to issue these requirements as a FMVSS under the National Traffic and Motor Vehicle Safety Act (Vehicle Safety Act),  the requirements must comply with that Act as well as the PSEA. The Vehicle Safety Act requires each safety standard to be performance-oriented, practicable,  and objective  and meet the need for safety. In addition, in developing and issuing a standard, NHTSA must consider whether the standard is reasonable, practicable, and appropriate for each type of motor vehicle covered by the standard.
As a FMVSS, the pedestrian alert sound system standard we are proposing today would be enforced in the same fashion as other safety standards issued under the Vehicle Safety Act. Thus, violators of the standard would be subject to civil penalties.  A vehicle manufacturer would be required to conduct a recall and provide remedy without charge if its vehicles were determined to fail to comply with the standard or if the vehicle's alert sound were determined to contain a safety related defect. 
Under the PSEA, the standard must specify performance requirements for an alert sound that enables blind and other pedestrians to reasonably detect EVs and HVs operating below their cross-over speed.  The PSEA specifies several requirements regarding the performance of the alert sound to enable pedestrians to discern the operation of vehicles subject to the Act. First, the alert sound must be sufficient to allow a pedestrian to reasonably detect a nearby EV or HV operating at constant speed, accelerating, decelerating and operating in any other scenarios that the Secretary deems appropriate.  Second, it must reflect the agency's determination of the minimum sound level emitted by a motor vehicle that is necessary to allow blind and other pedestrians to reasonably detect a nearby EV or HV operating below the cross-over speed.  NHTSA plans to ensure that EVs and HVs are detectable to pedestrians by specifying performance requirements for sound emitted by these vehicles so that they will be audible to pedestrians in the ambient noise environment typical of urban areas.
Nothing in the PSEA specifically requires the alert sound to be electrically generated. Therefore, if manufacturers wish to meet the minimum sound level requirements specified by the agency through the use of sound generated by the vehicle's power train or any other vehicle component, there is nothing in the PSEA to limit their flexibility to do so.
The alert sound must also reflect the agency's determination of the performance requirements necessary to ensure that each vehicle's alert sound is recognizable to pedestrians as that of a motor vehicle in operation.  We note that the requirement that the alert sound be recognizable as a motor vehicle in operation does not mean that the alert sound be recognizable as a vehicle with an internal combustion engine (ICE). The PSEA defines “conventional motor vehicle” as “a motor vehicle powered by a gasoline, diesel, or alternative fueled internal combustion engine as its sole means of propulsion.”  If Congress had intended the alert sound required by the PSEA to be recognizable as an ICE vehicle, Congress would have specified that the sound must be recognizable as a “conventional motor vehicle” in operation rather than a motor vehicle because Congress acts purposefully in its choice of particular language in a statute.  While the mandate that NHTSA develop performance requirements for an alert sound that is recognizable as a motor vehicle does not mean that the sound must be based solely on sounds produced by ICE vehicles, the mandate does impose substantive requirements that the agency must follow during the rulemaking. The Vehicle Safety Act defines a motor vehicle as a “vehicle driven or drawn by mechanical power and manufactured primarily for use” on public roads.  The requirement that the agency develop performance requirements for recognizability means that the pedestrian alert sound required by this standard must include acoustic characteristics common to all sounds produced by vehicles driven by mechanical power that make those sounds recognizable as a motor vehicle based on the public's experience and expectations of those sounds. For example, pitch shifting and increases in sound pressure level denote changes in speed and are common to all vehicles driven by mechanical power. Further, sounds that the public currently recognizes as generated by a vehicle driven by mechanical power have tonal components.
The PSEA mandates that the standard shall not require the alert sound to be dependent on either driver or pedestrian activation. It also requires that the safety standard allow manufacturers to provide each vehicle with one or more alert sounds that comply, at the time of manufacture, with the safety standard. Thus, a manufacturer may, if it so chooses, equip a vehicle with different sounds to denote different operating scenarios, such as reverse or start up. Each vehicle of the same make and model must emit the same alert sound or set of sounds. The standard is required to prohibit manufacturers from providing anyone, other than the manufacturer or dealers, with a device designed to disable, alter, replace or modify the alert sound or set of sounds emitted from the vehicle. A manufacturer or a dealer, however, is allowed to alter, replace, or modify the alert sound or set of sounds in order to remedy a defect or non-compliance with the safety standard. Additionally, vehicle manufacturers, distributors, dealers, and motor vehicle repair businesses would be prohibited from rendering the sound system inoperative under Section 30122 of the Vehicle Safety Act.
It is the agency's intention that the requirements of this standard be technology neutral. For this reason, we have chosen to establish minimum sound requirements for a vehicle-level test. The agency recognizes that, in the near term, most manufacturers would install speaker systems that emit synthetically developed sounds in order to meet the requirements of the proposed standard.
The agency interprets the requirement in the PSEA that each vehicle of the same make and model emit the same sound as applying only to sound added to a vehicle for the purposes of complying with this proposed standard. We also interpret the PSEA requirement that NHTSA prohibit manufacturers from providing anyone with a means of modifying or disabling the alert sound and the prohibition on making required safety systems inoperative contained in Section 30122 of the Vehicle Safety Act as applying only to sound added to a vehicle for the purposes of complying with this proposed standard.
Many changes to a vehicle could affect the sound produced by that vehicle. In issuing this proposal the agency does not wish to prevent manufacturers, dealers, and repair businesses from making modifications to a vehicle such as adding a spoiler or changing the vehicle's tires that may have the effect of changing the sound produced by the vehicle.
The agency will test to ensure sounds produced by two vehicles of the same model are the same (within 3 A-weighted dB) at the stationary condition so that a determination of the sameness of the sounds is not dependent on tire or wind noise or other factors that could influence a vehicle's sound output. The agency will not consider any modifications made to a vehicle that affect the mechanical, tire or wind noise produced by that vehicle to make an alert sound added to the vehicle inoperative.
The PSEA requires NHTSA to consider the overall community noise impact of any alert sound required by the new safety standard. In addition, NHTSA will consider the environmental analysis required by the National Environmental Policy Act (NEPA) when setting the standard.
As part of the rulemaking process, NHTSA is required to consult with various other organizations. This is further described in Section IV below.
In addition to requiring NHTSA to publish a final rule establishing the standard requiring an alert sound for EVs and HVs by January 4, 2014, the PSEA requires that the agency provide a phase-in period, as determined by NHTSA. However, full compliance with the standard must be achieved for all vehicles manufactured on or after September 1st of the calendar year beginning three years after the date of publication of the final rule. Thus, if the final rule were promulgated sometime in 2014, the three-year period after the date of publication of the final rule would end sometime in 2017. The first calendar year that would begin after that date in 2017 would be calendar year 2018. Thus, under that time scenario, full compliance would be required not later than September 1, 2018.
Finally, the PSEA requires NHTSA to conduct a study and report to Congress whether the agency believes that there is a safety need to require the alert sounds required by the FMVSS promulgated to meet the mandate of the Act for some motor vehicles with internal combustion engines. The report must be submitted to Congress by January 4, 2015. If NHTSA determines that there is a safety need to require alert sounds for those motor vehicles the agency must initiate a rulemaking to require alert sounds for them.
IV. Consultation With External Organizations Back to Top
NHTSA is required by the PSEA to consult with the following organizations as part of this rulemaking: The Environmental Protection Agency (EPA) to assure that any alert sound required by the rulemaking is consistent with noise regulations issued by that agency; consumer groups representing visually-impaired individuals; automobile manufacturers and trade associations representing them; technical standardization organizations responsible for measurement methods such as the Society of Automotive Engineers, the International Organization for Standardization, and the United Nations Economic Commission for Europe (UNECE), World Forum for Harmonization of Vehicle Regulations (WP.29).
The agency has established three dockets to enhance and facilitate cooperation with outside entities including international organizations. The first docket (No. NHTSA-2008-0108)  was created after the 2008 public meeting was held; it contains a copy of the notice of public meeting in the Federal Register, a transcript of the meeting, presentations prepared for the meeting and comment submissions. It also includes NHTSA's research plan, our “Notice of Intent to Prepare an Environmental Assessment for the Pedestrian Safety Enhancement Act of 2010” published on July 12th 2011 in the Federal Register, and the agency's Phase 1 and 2 research reports. (The Notice of Intent [NOI] and the agency's research are discussed more fully later in this document.) The second docket (No. NHTSA-2011-0100)  was created to collect comments on the NOI; it also includes a copy of that notice. The third docket (No. NHTSA-2011-0148)  was created in September 2011 to include materials related to the rulemaking process (“The Pedestrian Safety Enhancement Act of 2010”, Phase 1 and 2 research reports, statistical reports, meeting presentations, etc.), outside comments and items to be released in the future up to and including this Notice of Proposed Rulemaking.
NHTSA has since 2009 also been hosting a series of roundtable meetings with industry, technical organizations and groups representing people who are visually-impaired. Below are the dates and topics of discussion:
- April 14th, 2009: Status of Phase 1 research and industry updates.
- August 4th, 2009: Phase 1 research plan.
- January 25th, 2010: Final results of Phase 1 research and industry updates.
- June 24th, 2010: Phase 2 research plan and status of Phase 2 work.
- February 22nd, 2011: Final results of Phase 2 research. Attendees were asked to submit comments.
The following organizations have been participating in these meetings: The Alliance of Automotive Manufacturers, the Global Automakers (formerly Association of International Automobile Manufacturers (AIAM)), American Council of the Blind, The American Foundation of the Blind (AFB), the National Federation of the Blind (NFB), The International Organization for Standardizations (ISO), The Society of Automotive Engineers (SAE), the International Organization of Motor Vehicles Manufacturers (OICA), The Environmental Protection Agency (EPA) and Japan Automobile Manufacturers Association (JAMA).
Representatives of the EPA have also been included in our activities with outside organizations. They have been kept updated on our research activities and have actively participated in our outreach efforts. NHTSA has also kept up to date on EPA activities on the international front through the activities of the UNECE Working Party of Noise (GRB).
The American Foundation of the Blind, the American Council of the Blind and the National Federation of the Blind have provided NHTSA with invaluable information about visually-impaired pedestrian safety needs since the 2008 Public Meeting was held.
The Alliance of Automotive Manufacturers and Global Automakers (formerly the Association of International Automobile Manufacturers (AIAM)) have met separately with the agency to discuss our research findings and their ideas regarding this rulemaking. Members of both organizations have also met separately with the agency to discuss their own research findings and ideas for a potential regulatory approach to address the safety issues of interest to the agency.
Automotive manufacturers that produce EVs for the U.S. market have developed various pedestrian alert sounds, recognizing that these vehicles, when operating at low speeds, may pose an elevated safety risk to pedestrians. They have made vehicles with sound alert systems available for lease by NHTSA for research purposes. This information has been helpful in the agency decision making process.
The Society of Automotive Engineers (SAE) established the Vehicle Sound for Pedestrians (VSP) subcommittee in November 2007 with the purpose of developing a recommended practice to measure sounds emitted by ICE vehicles and alert sounds for use on EVs and HVs. Their efforts resulted in standard SAE J2889-1, Measurement of Minimum Noise Emitted by Road Vehicles.  The agency has been sending liaisons to the VSP meetings since 2008. SAE is the U.S. technical advisory group to the International Organization for Standardizations (ISO) and they both have cooperated in the development of the standard. The ISO document (ISO/NP 16254 Measurement of minimum noise emitted by road vehicles)  and SAE document are reported to be technically identical but this has not been confirmed by NHTSA at this time. The agency is currently using standard SAE J2889-1 and ISO10844  as references in the test procedure development.
The UNECE World Forum WP.29 determined that road transportation vehicles propelled in whole or in part by electric means present a danger to pedestrians and directed the Working Party on Noise (GRB) to assess what necessary steps WP.29 should take to help mitigate the problem. In response, GRB established an informal group on Quiet Road Transport Vehicles (QRTV)  to carry out the necessary activities to address the quieter vehicles issue and the potential need for global harmonization. NHTSA has been participating in the QRTV's meetings since its foundation in 2010 and has kept the group informed about ongoing agency research activities as well as the results from completed research studies.
At its March 2011 meeting, WP.29 adopted guidelines covering alert sounds for electric and hybrid vehicles that are closely based on the Japanese guidelines discussed more fully later in this document. The guidelines were published as an annex to the UNECE Consolidated Resolution on the Construction of Vehicles (R.E.3).
Considering the international interest and work in this new area of safety, the U.S. has proposed working on a new GTR, with Japan as co-sponsor, to develop harmonized pedestrian alert sound requirements for electric and hybrid-electric vehicles under the 1998 Global Agreement. WP.29 is now working to develop a GTR that will consider international safety concerns and leverage expertise and research from around the world. Meetings of the working group are planned to take place regularly with periodic reports to WP.29 until the expected establishment date for the new GTR in November 2014. NHTSA is currently leading the GTR development process.
Other international organizations, such as the International Organization of Motor Vehicles Manufacturers (OICA) and Japan Automobile Manufacturers Association (JAMA) have been providing NHTSA with their own research findings and have also been attending our quiet vehicle meetings.
V. Safety Problem Back to Top
A. Comparing the Vehicle to Pedestrian Crash Experience of ICE Vehicles and HVs and EVs
Passenger hybrid electric vehicles first became available to consumers in 2000, and their numbers as well as their proportion of the passenger vehicle fleet have risen every year since their introduction. According to the R.L. Polk and Company National Vehicle Population Profile, there were 18,628 registered passenger HVs in 2001. By 2004, there were 145,194 registered HVs comprising 0.1 percent of the passenger vehicle fleet. By 2009, the number had grown to 1,382,605 registered HVs comprising 0.6 percent of the fleet.
Advocacy groups have raised pedestrian safety concerns regarding HVs because a vehicle using an electric motor may be quieter than an ICE vehicle and may not emit the sounds that non-motorists rely on for warning as vehicles approach them. In 2009, NHTSA released the report “Incidence of Pedestrian and Bicyclist Crashes by Hybrid Electric Passenger Vehicles” which found that, when comparing similar vehicles, 77 out of 8,387 total HVs reported to be in any crash incident were involved in pedestrian crashes, and 3,578 out of 559,703 total ICE vehicles were involved in similar pedestrian crashes.  The report used data collected from 12 individual states. The years for which data was available varied across different states. Generally, the data used ranged from the years 2000 to 2006. HV crashes had an overall 40 percent higher chance to involve pedestrians. In situations involving certain low-speed maneuvers, HVs were twice as likely to be involved in a pedestrian crash as ICE vehicles in similar situations. The state data set that NHTSA used to determine the pedestrian and pedalcyclist crash rates for HVs did not include any information about the vision status of the pedestrians involved in the crashes. Therefore, we were unable to determine whether any of the pedestrians involved in these crashes were blind or visually impaired.
A recent analysis updated and verified these previous findings  by adding additional years of state crash files as well as by increasing the number of states included in the analysis from 12 to 16, with a total of 24,297 HVs (approximately three times the HVs of the 2009 study) and 1,001,000 ICE vehicles by Honda and Toyota, with five different models, in 16 States during 2000-2008. This updated analysis indicates that a total of 186 HVs and 5,699 ICE vehicles were involved in pedestrian crashes. A total of 116 HVs and 3,052 ICE vehicles were involved in crashes with bicycles. Overall, a statistical analysis referred to as odds ratios indicates that the odds of an HV being in either a pedestrian or bicycle crash is greater than the odds of an ICE vehicle being in a similar crash, 19 percent higher for pedestrian crash odds and 38 percent higher for bicycle crash odds.  The crash factors of speed limit, vehicle maneuver and location were examined to determine the relative incidence rates of HVs versus ICE vehicles and whether the odds ratio was different under different circumstances. This finding also indicates that the largest differences between the involvement of HVs and ICE vehicles in pedestrian crashes occur with speed limits of 35 mph and lower and during certain, typically low-speed, maneuvers such as making a turn, starting up, and pulling into or backing out of a parking space. HVs were about 1.38 times more likely to be involved in a pedestrian crash than a vehicle with an ICE after completing a low speed maneuver. The results in this updated analysis show trends similar to those first reported in our 2009 report. The sample sizes of pedestrian or bicycle crashes were verified to validate the sufficient statistical powers in this updated analysis.
The rate of crashes between HVs and pedalcyclists was different than the rate of crashes between HVs and pedestrians. While a larger percentage of pedalcyclist crashes for both HVs and ICE vehicles occurred at posted speed limits of 35 mph and below, the difference in rates of pedalcyclist crashes between HVs and ICE vehicles was higher at speed limits above 35 mph that at speed limits of 35 mph and below. For posted speed limits of 35 mph and below HVs showed an increased rate of pedalcyclist crashes when compared to ICE vehicles, however, the results were not statically significant. The difference in pedealcyclist crash rates between HVs and ICE vehicles was also greater when driving straight as compared to low-speed maneuvers.
This updated analysis further included all vehicle models from all manufacturers during the period covered by the study, beyond the five models from Toyota and Honda, and a similar pedestrian crash trend was also found from the expanded data. Comparisons restricted to HV and similar ICE pairs (Prius and Corolla; Civic HV and ICE model) only were also made. These comparisons also resulted in similar conclusions about HV pedestrian crashes relative to ICE vehicle pedestrian crashes, including that the odds of an HV being in a pedestrian crash is greater than the odds of an ICE vehicle being in a similar crash.
Despite the similarities in the overall sound level produced by the two vehicles, the differential crash rate for the Civic HV and the ICE version of the Civic was even larger than for other pairs of HVs and ICEs. We note that the HV Civic is much different than the other hybrid vehicles in the analysis because when the agency tested this vehicle, we could not get the ICE engine to shutoff even at idle. Thus, unlike the other HVs tested, the ICE was always on in this vehicle, but we acknowledge that in the real-world, the ICE may shut-off at some point. We do know that, although sound levels are similar, there are differences between the frequency profile of the HV and ICE Civics, but we do not know how pedestrians would perceive this difference either in general or in the low-speed maneuvers used in our crash analysis. The agency seeks comments on whether the differences in pedestrian crash rates between HVs and ICEs are solely due to a pedestrians' inability to detect the vehicle based on the vehicle's sound while operating below the crossover speed or whether there may be other factors that we have not identified that affect the difference in crash rates between the two types of vehicles.
While this updated analysis provides insightful comparisons of the incidence rates of HVs versus ICE vehicles involved in pedestrian crashes, there are some limitations to consider: the use of data from 16 states cannot be used to directly estimate the national problem size; there is still not enough data to draw conclusions in all scenarios of interest such as for individual low-speed maneuvers like making a turn, starting up, or in parking lots.
The Fatality Analysis Reporting System (FARS) contains a census of all traffic fatalities. HVs and EVs that struck and killed a pedestrian were identified using the Vehicle Identification Numbers (VINs) contained in the 2001 through 2009 FARS files. During this period, there were 53 pedestrian fatalities attributed to crashes involving 47 HVs and EVs. Almost all of these fatalities (47 of the 53) involved vehicles that were identified as passenger vehicles. In 2008, there were 10 HVs or EVs that struck and killed 10 pedestrians, and in 2009, there were 11 HVs or EVs that struck and killed 11 pedestrians.
However, these fatalities are not included in the target population for analysis under this rulemaking for two reasons. The first is that pedestrian fatalities are not as likely to occur at low speeds for which the rate of HV pedestrian collisions is significantly higher than collisions between ICE vehicles and pedestrians. This proposal would establish minimum sound requirements for hybrid and electric vehicles operating at speeds of 30 km/hr (18 miles per hour (mph)) and below. A majority of pedestrian fatalities occur when the vehicle involved in the collision is travelling at a speed greater than 18 mph. Overall, 67 percent of the pedestrian fatalities involving HVs or EVs and with known speed limits occurred at a speed limit above 35 mph. For all pedestrian fatalities with known speed limits, 62 percent occurred at a speed limit above 35 mph and 61 percent of those involving passenger vehicles occurred at a speed limit above 35 mph. The goal of this proposal is to prevent injuries to pedestrians that result from pedestrians being unable to hear nearby hybrid and electric vehicles. At speeds of 35 mph and above, at which a majority fatal crashes involving pedestrians occur, the sound levels produced by hybrid and electric vehicles are the same as the sound levels produced by ICE vehicles. Therefore, establishing minimum sound requirements for hybrid and electric vehicles operating at low speeds is not expected to have an impact on pedestrian fatalities.
The second reason is that the rate of pedestrian fatalities per registered vehicle for HVs and EVs is not larger (and is in fact lower) than that for ICE vehicles. Using 2008 data, the fatality rate for pedestrians in crashes with HVs and EVs is 0.85 fatalities per 100,000 registered vehicles, and the corresponding rate for ICE vehicles is 1.57 per 100,000 vehicles.
There also could be fatalities involving HVs and EVs that occur in non-traffic crashes in places such as driveways and parking lots. However, a comprehensive search for HVs and EVs involved in pedestrian fatalities could not be undertaken because NHTSA's Not in Traffic Surveillance (NiTS) system does not provide VINs, and a search for model names that indicate hybrid or electric vehicles did not identify any crashes involving pedestrian fatalities.
B. Need for Independent Mobility of People Who Are Visually Impaired
In addition to addressing the safety need in the traditional sense of injuries avoided as a result of preventing vehicle-pedestrian crashes, NHTSA believes it is important to note another dimension of safety that should be taken into account with respect to pedestrians who are blind or visually impaired. Pedestrians who are blind or visually impaired need to be able to travel independently and safely throughout their communities without fear of injury, both as a result of collisions with motor vehicles and as a result of other adverse events in the environments they must negotiate. To a far greater extent than is the case for sighted people, vehicle sounds help to define a blind or visually-impaired person's environment and contributes to that person's ability to negotiate through his/her environment in a variety of situations. 
Two long-established navigation aids that visually-impaired people use are the white cane and a guide dog. The modern white cane and the techniques for its use help the user to navigate and allow sighted people to recognize that a person is blind or visually impaired. Today, the “structured discovery” method of teaching independent travel for visually-impaired people emphasizes learning to use information provided by the white cane, traffic sounds, and other cues in the environment to travel anywhere safely and independently, whether the individual has previously visited the place or not.
Of the thirteen guide dog schools currently operating in the United States, most require applicants for guide dogs to have at least some skill in traveling with a long white cane, since the basic techniques for using a white cane and a guide dog are similar in many respects. A guide dog does not lead a person but simply guides him or her around obstacles; the handler is still responsible for navigation.
Whether a blind or visually-impaired person uses a white cane or guide dog, the primary purpose of both travel tools is to help the blind traveler identify and/or avoid obstacles in his or her path using the sense of touch. The remaining information needed by a blind or visually-impaired person to travel safely and independently is provided primarily through the sense of hearing.
When traveling with a white cane or guide dog, the primary sound cue used by blind pedestrians is the sound of vehicle traffic, which serves two purposes: navigation and collision avoidance. Navigation involves not only ascertaining the proper time to enter a crosswalk and maintain a straight course through an intersection while crossing, but also the recognition of roadways and their traffic patterns and their relationship to sidewalks and other travel ways a blind or visually-impaired person might use.
Sound emitted by individual vehicles, as opposed to the general sound of moving traffic, is critical. The sound of individual vehicles alerts blind travelers to the vehicle's location, speed, and direction of travel. For example, a blind or visually-impaired person moving through a parking lot can hear and avoid vehicles entering or exiting the lot or looking for parking spaces; a blind person walking through a neighborhood can hear when a neighbor is backing out of a driveway. The vehicle sound also indicates to a blind or visually-impaired pedestrian whether a vehicle is making a turn, and if so, in which direction. The sound of individual vehicles also allows the blind traveler to detect and react to unusual or unexpected vehicle movement.
The sound of a vehicle that has an activated starting system but is stationary (usually referred to as “idling” for vehicles with internal combustion engines) alerts the blind or visually-impaired traveler to the fact that the vehicle is not simply parked and that it may move at any moment. The sound of a vehicle starting is important for the same reason. If a blind person is approaching a driveway and notes a vehicle that is stationary but running, or hears a vehicle start, he or she will wait for the vehicle to pull out, or for an indication that it will not, for example by noting that the vehicle remains stationary for some time, indicating that the driver has no immediate plans to move.
Because traffic sound is a navigation aid for blind and visually-impaired pedestrians, as well as an indispensable part of traveling safely, blind people listen to the sound of traffic actively and constantly when they are walking, even when they are not at an intersection. The sound of traffic helps blind individuals follow the roadway; this is critical, even when there is a sidewalk, to keep the blind individual on course. Traffic sounds also allow the detection of roadway changes like curves, forks, or merges. The sound of traffic is particularly important in negotiating intersections. By listening to the traffic, a blind or visually-impaired traveler can determine how the intersection is controlled (traffic signal, stop sign, etc.); how many lanes of traffic are involved; and any unusual characteristics of the intersection (e.g., three-way intersections or roundabouts). These determinations can be made by listening to the sounds of vehicle engines—often through one or two entire signal cycles—to determine driver behavior, which is usually a reliable indicator of the characteristics of the intersection. This includes the sound of stationary vehicles—particularly in multi-lane or oddly shaped intersections—because it is important to identify which lanes of traffic are active, when, and for how long; and to then follow the line of traffic that most nearly parallels the direction in which the traveler wishes to proceed. At the same time that the blind traveler is listening to the overall traffic pattern, he or she also listens for cues from individual vehicles, particularly when determining the precise moment to enter the crosswalk. At signaled intersections, an idling vehicle in the street parallel to the path of the traveler that accelerates and moves through the intersection is an indication that a traffic signal has just changed and that it is safe to proceed into the cross street, with maximum time to complete the crossing. In general, by crossing when the traffic flow is parallel to him or her, a blind individual can safely cross most intersections without difficulty. The individual will use the sound of the parallel traffic while crossing to maintain a roughly straight line through the intersection. Figure 1 shows several examples of how a blind pedestrian would use the sound of traffic to cross a complex intersection.
Example 1: Back to Top
A blind pedestrian standing at corner A (facing corner B) ready to cross, will wait for the stationary vehicles behind him/her to start moving as an indication that the traffic light has changed. Then, the pedestrian will proceed to cross the street and follow the parallel line of traffic on his left (from A to B) confident there is enough time to safely cross the street.
Example 2: Back to Top
A blind pedestrian standing at corner A (facing corner C) ready to cross, will use the sound of the stationary vehicles on his/her left and the parallel traffic on his/her right as guides to follow a straight path while crossing.
Example 3: Back to Top
A blind pedestrian at corner C (facing corner D) ready to cross, will wait for the traffic from C to A to stop and the parallel traffic across the intersection to start, to safely walk from corner C to Corner D. The sounds from the stationary vehicles on his/her left and the parallel traffic across the intersection serve as guides to keep a straight path while crossing.
Using the white cane or guide dog and the sound of traffic, people who are blind or visually-impaired have been able to navigate safely and independently for decades. Blind and visually-impaired people travel to school, the workplace, and throughout their communities to conduct the daily functions of life primarily by walking and using public transportation. Safe and independent pedestrian travel is essential for blind or visually-impaired individuals to obtain and maintain employment, acquire an education, and fully participate in community life. Short of constantly traveling with a human companion, a blind or visually-impaired pedestrian simply cannot ensure his or her own safety or navigate effectively without traffic sound. To the extent that there are more and more HVs and EVs on the road that are hard to detect, people who are blind or visually impaired will lose a key means—the sound of traffic—by which they determine when it is safe to cross streets, but also by which they orient themselves and navigate safely throughout their daily lives, avoiding dangers other than automobiles.
VI. NHTSA Research and Industry Practices Back to Top
On May 6, 2009 NHTSA issued a research plan describing the research relating to quieter vehicles it planned to conduct. This section reports on the research completed to date.
A. NHTSA Phase 1 Research 
In April 2010 NHTSA released a report titled “Quieter Cars and the Safety of Blind Pedestrians: Phase 1” referred to as Phase 1. This report documented a study conducted by the John A. Volpe National Transportation Systems Center (Volpe) under an interagency agreement. This study documents the overall sound levels and general spectral content for a selection of HVs and ICE vehicles in different operating conditions, evaluates vehicle detectability for two ambient sound levels, and considers countermeasure concepts. The study investigated operating scenarios of concern for pedestrians who are blind or visually impaired, documented acoustic measurements of hybrid, electric and ICE vehicles and ambient environments in which blind or visually impaired pedestrians might reasonably be expected to make travel decisions based on sound alone, examined the auditory detectability of vehicles in safety scenarios of concern to individuals who are blind or visually impaired and examined potential countermeasures.
Safety Scenarios for Pedestrians Who Are Blind or Visually-Impaired
As part of Phase 1 research NHTSA sought to identify operating scenarios necessary for the safety of visually-impaired pedestrians. The researchers identified these scenarios based on crash data, literature reviews, and unstructured conversations with blind pedestrians and orientation and mobility specialists. Scenarios were defined by combining pedestrian vehicle environments, vehicle type, vehicle maneuver/speed/operation, and considerations of ambient sound level. The operating scenarios identified in Phase 1 are:
- Vehicle approaching at low speed: One of the strategies used by pedestrians who are blind is to cross when the road is quiet. This technique assumes that it is safe to proceed when a vehicle is loud enough to be heard far enough away, there are no other masking sounds present, and no other vehicles are detected.
- Vehicle backing out (as if coming out of a driveway): There is a concern quieter vehicles may not be detectable when backing out. This scenario is complex for pedestrians since it is difficult to anticipate where there may be a driveway and the driver's visibility may be limited. The pedestrian may have limited time to react and respond to avoid a conflict.
- Vehicle travelling in parallel and slowing: Pedestrians who are blind often need to distinguish between a vehicle moving through an intersection and a vehicle turning into their path. The pedestrian needs to perceive this information when the vehicle is in the parallel street, before it turns into his or her path. The sound of slowing vehicles in the parallel street helps pedestrians identify turning vehicles.
- Vehicle accelerating from stop: Pedestrians who are blind use the sound of traffic in the parallel street to establish alignment and to identify a time to cross. The sound of accelerating vehicles in the parallel street indicates, for example, that the perpendicular traffic does not have the right of way and thus a crossing opportunity is available. Pedestrians may initiate their crossing as soon as they detect the surge of parallel traffic or may delay the decision to make sure traffic is moving straight through the intersection and not turning into their path. A delay in detecting the surge of parallel traffic may impact the opportunity to complete a crossing within the designated walking interval.
- Vehicle stationary: The sound of vehicles idling provides important cues. For example, the sound of a vehicle in the far lane gives cues about the width of the road (number of lanes), and conveys information about the distance to walk and the time needed to navigate across the street. A quieter vehicle may not be detected when it is stationary at intersections or parking lots and it may start moving suddenly at the same time a pedestrian enters the conflicting path.
NHTSA was able to gather crash data for collisions involving pedestrians and HVs when the HV was operating in one of the scenario described above (the crash report did not separately analyze vehicle starting from a stop and the vehicle stationary conditions) immediately prior to the crash in both the crash report released by NHTSA in September of 2009  and the updated crash report released in October 2011.  The 2011 report analyzed the crash rates for vehicles making a turn, slowing/stopping, backing, entering and leaving a parking space/driveway and starting in traffic separately and then analyzed all those operating conditions together. Because of the sample size an independent odds ratio was not available for any of the scenarios. When taken together, however, these low speed operating conditions show a statistically significant 1.38 odds ratio showing an increased risk of pedestrian collisions.
For this study, the sounds emitted by HVs and ICE vehicles were measured and recorded under operating conditions representative of the previously identified safety scenarios.  The operating conditions were as follows: (1) a vehicle backing up at 5 mph (mimicking a vehicle backing out of a driveway); (2) a vehicle slowing from 20 to 10 mph (mimicking a vehicle preparing to turn right from the parallel street); (3) a vehicle approaching at a low constant speed (6 mph and 10 mph); (4) a vehicle accelerating from a stop; and (5) a vehicle idling. Average A-weighted sound levels for each of the six vehicles tested are reported in Table 1.
|Scenario/vehicle operation||2010 Toyota Prius||2009 Toyota Matrix||Honda Civic Hybrid||Honda Civic ICE||2009 Toyota Highlande Hybrid||2008 Toyota Highlander|
|[Average A-weighted level, LAeq0.5s, dB]|
|Approaching at 6 mph||44.7||53.5||49.3||52.0||53.2||55.5|
|Backing out (5 mph)||44.2||51.3||48.5||58.2||45.9||52.7|
|Slowing from 20 to 10 mph||53.0||54.2||56.6||55.0||53.0||55.4|
|Idling or Stationary but activated||1||47.8||44.8||46.0||1||48.1|
Additionally, measurements were collected for vehicles approaching at moderate constant speeds (20 mph, 30 mph, and 40 mph) in order to document the convergence, if any, of HVs and ICE vehicles at higher speeds. In general, HVs were quieter below approximately 20 mph, above which either the vehicle's ICE engine turned on, tire and road noise became dominant, or both. HVs also tended to have less high frequency content than ICEs at low speeds. Further details and results from this study can be found in NHTSA's final report DOT HS 811 304. 
Auditory Detectability of Vehicles in Critical Safety Scenarios 
In Phase 1, NHTSA compared the auditory detectability of HVs and ICE vehicles by pedestrians who are legally blind. Forty-eight independent travelers, with self-reported normal hearing, listened to binaural  audio recordings of two HVs and two ICE vehicles in three operating conditions, and two different ambient sound levels. The operating conditions included a vehicle: approaching at a constant speed (6 mph); backing out at 5 mph; and slowing from 20 to 10 mph (as if to turn right). The ambient sound levels were a quiet rural (31.2 dB (A)) and a moderately noisy suburban ambient (49.8 dB (A)). Overall, participants took longer to detect the two HVs tested (operated in electric mode), except for the slowing maneuver. Vehicle type, ambient level, and operating condition had a significant effect on response time.
Data collection included missed detection frequency and response time (and corresponding time-to-vehicle arrival and detection distance). Missed detection frequency is defined as instances when the target vehicle is present and the participant fails to respond. Response time is computed as the time from the start of a trial to the instant the participant presses a space bar as an indication he/she detects the target vehicle. Time-to-vehicle-arrival is the time from first detection of a target vehicle to the instant the vehicle passes the microphone line/pedestrian location. Detection distance is the longitudinal space between the vehicle and the pedestrian (microphone) location at the instant the participant indicated detection of a target vehicle.
A repeated measure of analysis of variance (ANOVA) was used to analyze the main and interaction effects of the independent variables: vehicle type, vehicle maneuver and ambient sound level. A separate analysis was completed for each scenario, and a pair-wise t-test compared each vehicle with the other (ICE vehicle and HV twins) for each ambient sound level. The time-to-vehicle arrival for each vehicle-ambient condition is shown in Table 2, Table 3 and Table 4 for each of three scenarios.
Vehicle Approaching at 6 mph (9.6 km/h) Pass by: The first traveling situation examined was a pedestrian standing on the curb waiting to cross a one-way street when there may be vehicles approaching from the left. Some trials included a target vehicle and some trials only included background noise. The target vehicle in this scenario was traveling from the left at a constant speed of 6 mph. There were vehicles in the background in all trials. The pedestrian had to be able to detect a vehicle that would affect the decision about when to start to cross the street. This scenario tested the distance and time at which a pedestrian can detect a vehicle approaching at low speed. On average, participants took 1.1 seconds longer to detect vehicles in the high ambient sound condition than in the low ambient sound condition. The main effect of ambient was statistically significant. The mean time-to-vehicle-arrival was 5.5 and 4.3 seconds for the low and high ambient condition respectively. Participants detected both ICE vehicles sooner than the HV twins. The main effect of vehicle type was statistically significant. The interaction effect of vehicle type and ambient was also statistically significant, meaning that the difference between when a passenger was able to detect an ICE vehicle versus its HV twin was greater when ambient was high than when it was low. Table 2 presents the individual differences between ICE vehicles and their HV peers (i.e., Prius vs. Matrix and Highlander hybrid vs. Highlander ICE); pair-wise comparisons are statistically significant within a given ambient condition. Participants were more likely to miss the Toyota HVs than the Toyota ICE vehicles approaching at a constant low speed. The missed detection rates in the low ambient condition were: 0.02 for the Prius; 0.01 for the Matrix; 0.03 for the Highlander Hybrid; and 0.0 for the Highlander ICE vehicle. The corresponding values in the high ambient condition were: 0.21 for the Prius; 0.02 for the Matrix; 0.04 for the Highlander; and 0.01 for the Highlander ICE vehicle.
|Vehicle||Ambient sound level||Time-to-vehicle arrival (s)||Detection distance (ft)|
|2010 Toyota Prius||Low||4.3||37.9|
|2009 Toyota Matrix||Low||5.5||48.4|
|2009 Highlander Hybrid||Low||5.3||46.6|
|2008 Highlander ICE||Low||6.8||59.4|
Vehicle Backing Out (5 mph (8 km/h) Reverse): The second traveling situation was a pedestrian walking along a sidewalk with driveways on the left side; the pedestrian heard distant vehicles in the background in all trials. This is similar to walking in an area that is a few blocks away from a main road. The target vehicle was a nearby vehicle backing towards the pedestrian at a constant speed of 5 mph. This task is complex for pedestrians since it is difficult to anticipate where there may be a driveway and when a vehicle will move out of a driveway. In addition, a driver's visibility may be limited and the pedestrian may have very limited time to respond to avoid a conflict. The main effect of ambient was statistically significant. The average time-to-vehicle-arrival was 4.4 and 2.7 seconds for the low and high ambient condition, respectively. Participants took longer to detect both HVs than their ICE twins. The main effect of vehicle type was statistically significant. Table 3 shows the individual differences between ICE vehicles and their HV twins; pair-wise comparisons were statistically significant within a given ambient condition. Participants were more likely to miss the Toyota HVs than the Toyota ICE vehicles in the backing out session. The missed detection rates in the low ambient condition were: 0.05 for the Prius; 0.02 for the Matrix; 0.10 for the Highlander Hybrid; and 0.02 for the Highlander ICE. The corresponding values in the high ambient condition were: 0.11 for the Prius; 0.0 for the Matrix; 0.26 for the Highlander; and 0.02 for the Highlander ICE. On average, participants took longer to detect vehicles in the high ambient sound condition than in the low ambient sound condition.
|Vehicle||Ambient sound level||Time-to-vehicle arrival(s)|
|2010 Toyota Prius||Low||4.0|
|2009 Toyota Matrix||Low||5.2|
|2009 Highlander Hybrid||Low||3.3|
|2008 Highlander ICE||Low||5.2|
Vehicle Traveling in Parallel Lane and Slowing (Slowing from 20 to 10 mph (32 to 16 km/h): The third and last traveling situation examined in the study was a pedestrian trying to decide when to start crossing a street with the signal in his/her favor and a surge of parallel traffic on the immediate left. The sound of slowing vehicles in the parallel street helps blind pedestrians identify turning vehicles. In some trials (no-signal condition), a vehicle continued straight through the intersection at 20 mph, so pedestrians can cross whenever they choose. However, in other trials there was a vehicle slowing from 20 mph to 10 mph as if to turn right into the pedestrian path (target vehicle). The pedestrian had to be able to detect when the vehicle was slowing. This scenario tests whether the pedestrian perceived this information when the vehicle was in the parallel street. Participants were more likely to miss the ICE vehicles approaching in the parallel lane and slowing than the HVs in the same situation. Table 4 shows the time-to-vehicle arrival and detection distance for the `vehicle slowing' scenario. Pair-wise comparisons (HV vs. ICE twin) were statistically significant within a given ambient condition. On average, participants detected HVs sooner than their ICE vehicle twins. The main effect of vehicle type was statistically significant. The trend observed in the vehicle-slowing scenario (i.e., HVs are detected sooner than their ICE vehicle twins) may be explained by a noticeable peak in the 5000 Hz one-third octave band for the HVs tested during this operation. The tone emitted was associated with the electronic components of the vehicles when braking (e.g., regenerative braking). The missed detection rates in the low ambient condition were: 0.05 for the Prius; 0.31 for the Matrix; 0.03 for the Highlander Hybrid; and 0.17 for the Highlander ICE vehicle. The missed detection rates in the high ambient condition were: 0.05 for the Prius; 0.35 for the Matrix; 0.03 for the Highlander Hybrid; and 0.17 for the Highlander ICE vehicle.
|Vehicle||Ambient sound level||Time-to-vehicle arrival(s)||Detection distance (ft)|
|2010 Toyota Prius||Low||2.0||35.9|
|2009 Toyota Matrix||Low||1.1||18.0|
|2009 Highlander Hybrid||Low||3.0||58.8|
|2008 Highlander ICE||Low||1.5||25.7|
Table 5 shows the time-to-vehicle arrival by vehicle type, and ambient condition. Considering all three independent variables, there was a main effect of vehicle, vehicle maneuver, and ambient sound level. Similarly, there were interaction effects between vehicle type and ambient; vehicle type and maneuver, ambient and vehicle maneuver, and a three way interaction between ambient, vehicle type and vehicle maneuver.
|Scenario||Low ambient||High ambient|
|HVs||ICE Vehicles||HVs||ICE Vehicles|
|Approaching at 6 mph||4.8||6.2||3.3||5.5|
|Backing out (5 mph)||3.7||5.2||2.0||3.5|
|Slowing from 20 to 10 mph||2.5||1.3||2.3||1.1|
B. NHTSA Phase 2 Research
In October 2011 NHTSA released a second report examining issues involving hybrid and electric vehicles and blind pedestrian safety titled “Quieter Cars and the Safety of Blind Pedestrians, Phase 2: Development of Potential Specifications for Vehicle Countermeasure Sounds.” The research conducted by Volpe first sought to define acoustic specifications to be used as alert sounds for quiet vehicles based on the sounds produced by ICE vehicles. Volpe then analyzed the loudness of the ICE sounds in a suburban ambient using psychoacoustic modeling. Volpe used human subject testing to evaluate the performance of several different varieties of countermeasure sounds including ICE sounds. Based on the results from the Phase I research, the psychoacoustic modeling and the human subjects testing Volpe developed potential specifications for vehicle countermeasure sounds.
The Phase 2 research developed various options and approaches to specify vehicle sounds that could be used to provide information at least equivalent to the cues provided by ICE vehicles, including speed change. In this research, acoustic data acquired from a sample of 10 ICE vehicles was used to determine the sound levels at which synthetic vehicle sounds, developed as countermeasures, could be set. ICE-equivalent sounds were specified as overall A-weighted sound levels and spectral content at the one-third octave band level. Psychoacoustic models and human-subject testing were used to explore issues of detectability, masking, and recognition of ICE-like and alternative sound countermeasures.
The researchers determined that the elements of a specification for vehicle sounds should consider sound output levels; pitch changes that convey changes in vehicle speed; and acoustic qualities that determine whether the sound is perceived as a vehicle. The options discussed in the Phase 2 final report  assume that the vehicle acoustic countermeasure should:
- Provide information at least equivalent to that provided by ICE vehicles, including speed change; and
- Provide for detection of a vehicle in residential, commercial and other suburban and urban environments. Note: Human-subject tests for Phase 2 were conducted in an ambient level of approximately 58-61 dB (A).
Phase 2 work focused initially on the following two ideas: (1) the lack of detectability of quieter vehicles can be remediated if they are fitted with synthetic sound generators that emulate the sound of typical ICEs; and (2) the specifications for the vehicle sounds can be defined in terms of objective parameters—namely, overall sound output as measured by the SAE J2889-1 procedure and spectral distribution specifications for the minimum amount of sound level in one-third-octave bands.
Recognizability is more complex than detectability. Most sounds, and sounds as complex as those emitted by an ICE, have numerous properties in addition to loudness and spectral distribution that affect human perception. Among these properties are rise time, decay time, repetition rates, variations in pitch and loudness, and phase relations among various components of the sound. These challenges can be demonstrated, for example, by playing a recording of a sound backwards, for example, that changes in these properties can render a sound unrecognizable even though loudness and spectral distribution are unchanged. There are no established quantitative metrics for many qualities of a sound that a person might use for recognition.
In the Phase 2 report Volpe first considered whether HVs and EVs should be equipped with sounds that are based on the acoustic profile of ICE vehicles. This concept is based on the assumption that the ICE vehicles measured in this study are typical of the current fleet, emit an acceptable amount of noise during low-speed operations, and that some (e.g., ICE-like) countermeasure sounds can be based on the statistical average of real-vehicle spectral characteristics. Researchers developed the potential specifications for alert sounds shown in Table 6 and Table 7 based on acoustic analysis of sounds produced by ICE vehicles to demonstrate what acoustic specifications for a vehicle alert sound might look like. The derivations of these data are given in Section 5 of the Phase 2 final report.
|Vehicle operation||L Aeq, 1/2 sec, dB(A)|
|Stationary but activated||55.2|
Table 7 shows the corresponding minimum A-weighted one-third-octave-band spectra for each operating mode. ICE vehicles have energy components in all frequencies (e.g., 100 to 20k Hz), however, the psychoacoustic models implemented in this study show that energy components in the one-third octave bands ranging from 1600 Hz to 5000 Hz contributed the most to detection, and those ranging from 315 Hz to 1600 Hz contributed additional detection and pitch information. These spectral distribution limits are derived from the procedures described in Section 6 of the Phase 2 final report.
|1/3 Octave band center frequency, Hz||6 mph||10 mph||15 mph||20 mph||Acceleration||Startup||Stationary but activated|
|100 to 20000||61.1||63.6||68.1||70.2||66.7||70.7||55.2|
The Volpe Center examined two options  under this first concept (ICE-like sounds):
Recordings of Actual ICE Sounds
The first option under the ICE-like sound concept explored using recordings of actual ICE vehicles as alert sounds. Recordings would be made when the vehicle is operating at constant speeds, forward from 0 to 20 mph and in reverse at 6 mph. Other components of the vehicles noise output (e.g., tire noise, aerodynamic noise, AC fan noise) would be emitted regardless of whether an ICE is in use and would not be included in these recordings. Sound generation systems with signal processing capabilities would be used to continuously and monotonically vary the sounds from one operating condition to the next according to vehicle input (e.g. vehicle speed sensors, throttle sensors, etc.). In this option, emitted sounds would be based on standardized recordings with processing limited to pitch shifting in proportion to vehicle speed and interpolation between sounds.
Synthesized ICE-Equivalent Sounds
The second option under the ICE-like sound concept explored using simulated ICE sounds directly synthesized by a digital-signal processor (DSP) programmed to create ICE-like sounds (based on actual target sounds) that would vary pitch and loudness depending on vehicle inputs. This is in contrast to the first option, described above, in which the sounds come directly from recordings of actual vehicles, and the processor must store and interpolate among files representing every mode of operation and for every speed within the 0 to 20-mph range. Here, the resulting synthesized sounds would resemble those of the first option, but have fewer spectral components. A synthesizer could be simpler and cheaper than a sound generator based on real ICE sounds. For this option, target sounds, recorded from actual vehicles for the operations specified above would be used. The synthesized sounds would then be developed to match the spectral shape of these target sounds. (Note: by definition, power-spectra spectral lines have a resolution of 1 Hz).
Sound generation systems with signal processing capabilities would be used to continuously and monotonically vary the sounds from one operating condition to the next according to vehicle input (e.g. vehicle speed sensors, throttle sensors, etc.) and the synthesis algorithms developed for their sounds. The two options listed above assume that band-limited (315 Hz to 5000 Hz) ICE-like sounds will be recognizable as motor vehicles.
Alternative, Non-ICE-Like Sounds Designed for Detectability
The second concept, described in the Phase 2 final report, consists of alternative countermeasure sounds with acoustic characteristics different from ICE vehicles. Some of the countermeasures evaluated in the human-subject studies have sound characteristics that could improve detectability when compared to ICE-equivalent sounds. The following sound characteristics can improve detectability of a sound source  :
- Pulsating quality with pulse widths of 100 to 200 msec.
- Inter-pulse intervals of about 150 msec.
- Fundamental tonal component in 150 to 1000 Hz range.
- At least three prominent harmonics in the 1 to 4 kHz range.
- Pitch shifting denoting vehicle speed change.
The design of a non-ICE sound involves a complex tradeoff among several factors including annoyance, cost, detectability, and overall sound pressure level values. While the required sound pressure level values for non-ICE-like sounds will generally be lower than for ICE-like sounds for the same detection distance, there is no objective basis upon which to calculate the difference in sound pressure level values for the class of non-ICE sounds as a whole. Rather, the equivalent detectability sound pressure level value for a particular non-ICE sound must initially be determined experimentally by a jury process that rates detectability. As psychoacoustic models improve, it may be possible to use them in place of jury testing to determine minimum sound pressure level specifications for these sounds, but that approach is not yet sufficiently accurate.
In this concept sound generation systems with signal processing capabilities would be used to continuously and monotonically vary the pitch and amplitude of sounds as appropriate to operating conditions according to vehicle inputs (e.g. vehicle speed sensors, throttle sensors, etc.). The appropriate relationship between sound amplitude and throttle position would need to be determined. The detectability of a specific non-ICE sound can be best determined only through human subjects testing, at the present state of the art.
Hybrid of Options Discussed Above
A third concept to designing countermeasure sounds, explored in the Phase II report, would be a combination of the concepts (i.e. using ICE-like or non-ICE-like sounds) discussed above, with the goal of gaining the benefits of each, while minimizing the disadvantages. Simulated ICE sound could be generated which would vary pitch and loudness depending on vehicle inputs. This system could simultaneously generate both ICE-like sounds at a lower sound pressure level than the concepts based on ICE sounds discussed above, and synthetic sounds designed for optimal alerting potential with minimal annoyance. The ICE-like sound components may not be heard in higher urban ambient-noise conditions, but their association with the alerting sound would be learned over time from when the pedestrian is exposed to the sound in lower ambients. This method would most likely depend on jury testing of human subjects to set the sound level for detection.
Human Subject Evaluation of Detectability
A human subject study was conducted to compare the auditory detectability of potential sounds for hybrid and electric vehicles operating at a low speed. The sounds evaluated included: (1) Sounds produced by vehicles with integrated sound systems rented from manufacturers, and (2) sounds produced by prototype systems rented from manufacturers, and played back by loudspeakers temporarily mounted on HVs rented separately. Five vendors, motor vehicle manufacturers or suppliers of automotive electronics, provided prototypes of synthetic sound generators for EVs or HVs. The five systems were labeled “A” to “E”. A total of nine sounds were evaluated: A1, A2, A5, B, C, D, E1, E3, and E4. Sounds were evaluated at two sound pressure levels typical of ICE vehicles at low speeds (i.e., A-weighted SPL of 59.5 dB and 63.5 dB).  An ICE vehicle that produced A-weighted SPL of 60 dB in the 6 mph pass-by test was used as a reference in this evaluation. The ICE vehicle was labeled `R'.
Sound A1 was an engine like sound with a turbine-like whine that had a prominent peek that varied from 150 Hz to 300 Hz based on vehicle speed. Sound A2 was an engine sound with enhanced valve noise with prominent signal content between 100 Hz and 200 Hz. Sound A5 was a whirring sound with a diesel engine sound. The fundamental signal content of the whirring part of the sound for sound A5 was between 400 Hz and 600 Hz based on vehicle speed. Sound B emulated the exhaust note (the fundamental of the combustion noise) of an engine. The sound did not contain appreciable components above 250 Hz. Sound C was a Wavy, turbo-like sound with most of its energy as broadband noise in the 200 Hz to 5000 Hz range. Sound D was a broadband sound designed to suggest an electric motor coupled to other rotating machinery. Sound E1 was a pure engine noise with most of its energy below 300 Hz. Sound E3 was an engine-like sound with a `whirring' character and a flatter spectral distribution than Sound E1 and had none of the prominent harmonics of the combustion note. Sound E4 contained short bursts of predominantly high-frequency sound with the peak amplitude of the fundamental varying in frequency from about 450 Hz to 700 Hz based on speed.
Data was collected outdoors during three independent sessions conducted on three days in July and August 2010. The first session included four operating modes: idle (stationary), acceleration from stop, start-up and 6 mph forward pass-by. The following two sessions included the 6 mph forward pass-by. The HVs used in the study were operated in electric mode during the pass-by trials. The sample included 79 participants 34 of which were sighted and 45 of which were legally blind. The legally blind participants were independent travelers and all participates had self-reported normal hearing.
The study took place in a parking lot located on the USDOT/Volpe Center campus in Cambridge, Massachusetts. The test site has the acoustic characteristic of an urban area with a typical ambient noise of approximately A-weighted sound pressure level of 58-61 dB. The dependent variables examined in the study included raw detection distance, proportion of detection, time-to-vehicle arrival, and detection distance. Raw detection distance is the number of feet the vehicle was from the participant when the participant indicated she or he heard the sound. A failure to detect the sound before the vehicle passed was treated as missing data. Proportion of detection is the proportion of trials of a given condition in which the participant detected the sound anytime before the vehicle passed the participant. Time-to-vehicle-arrival is the time, in seconds, from detection of a target vehicle sound to the instant the vehicle passes the pedestrian location. Detection distance is the calculated distance, feet, to the target vehicle at the moment each subject responded.
Each subject had a push button device which they used to indicate when they detected a nearby vehicle. Participants were asked to press a response button when they detected and recognized a vehicle that would affect their decision about when to start crossing the street.
Table 8 shows the mean detection distances for the sounds evaluated in the human-subject studies for the 6 mph pass-by; sounds at the top of the list can be described as sounds designed according to psychoacoustic principles and sounds at the end of the list can be described as ICE-like sounds with only the fundamental combustion noise or otherwise lacking in the qualities that support detectability. The results show that high amplitude sounds (A-weighted SPL of 63.5 dB) were detected more often and at greater distances than low amplitude sounds (A-weighted SPL of 59.5 dB).
|Sound number||Average detection distance (feet) for amplitude equal 59.5 dB(A)||Average detection distance (feet) for amplitude equal 63.5 dB(A)|
|ICE vehicle, 60 dB(A)||41||NA|
Results show that