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Compliance with Interstate Motor Carrier Noise Emission Standards: Exhaust Systems

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Information about this document as published in the Federal Register.

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Federal Motor Carrier Safety Administration (FMCSA), DOT.


Notice; request for comments.


FMCSA requests public comment on the merits of a petition for rulemaking filed by the Truck Manufacturers Association. This trade association, whose members include all of the major North American manufacturers of medium and heavy-duty trucks, has petitioned FMCSA to amend the Federal Motor Carrier Safety Regulations to eliminate turbochargers from the list of equipment considered to be noise dissipative devices. The Truck Manufacturers Association contends that virtually all trucks are now equipped with turbochargers. Hence, these trucks cannot be cited for failure to meet the visual exhaust system inspection requirements of FMCSA's safety regulations if they have no muffler.


Comments must be received on or before October 25, 2006.


You may submit comments [identified by DOT DMS Docket No. FMCSA-2006-24065] by any of the following methods:

  • Web site: Follow the instructions for submitting comments on the DOT electronic docket site.
  • Fax: 1-202-493-2251.
  • Mail: Docket Management Facility, U.S. Department of Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401, Washington, DC 20590-0001.
  • Hand Delivery: Room PL-401 on the Plaza Level of the Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.
  • Federal eRulemaking Portal: Go to Follow the online instructions for submitting comments.

Instructions: All submissions must include the Agency name and docket number for this notice. Note that all comments received will be posted without change (including any personal information provided) to See the Privacy Act heading for further information.

Docket: For access to the docket to read background documents or comments received, go to at any time or to Room PL-401 on the Plaza Level of the Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management System (DMS) is available 24 hours each day, 365 days each year. If you want to be notified that we received your comments, please include a self-addressed, stamped envelope or postcard or print the acknowledgement page that appears after submitting comments online.

Privacy Act: Anyone may search the electronic form of all comments received into any of DOT's dockets by the name of the individual submitting the comment (or of the person signing the comment, if submitted on behalf of an association, business, labor union, or other entity). You may review DOT's complete Privacy Act Statement in the Federal Register published on April 11, Start Printed Page 558232000 (65 FR 19476). This statement is also available at

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Mr. Michael Huntley, Division Chief, Vehicle and Roadside Operations Division (MC-PSV), Office of Bus and Truck Standards and Operations, phone (202) 366-4001, e-mail

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On October 21, 1974, the Environmental Protection Agency (EPA) issued final regulations establishing the Interstate Motor Carrier Noise Emission Standards for maximum external noise emissions of motor vehicles having a gross vehicle weight rating (GVWR) or a gross combination weight rating (GCWR) of more than 10,000 pounds that are operated by commercial motor carriers engaged in interstate commerce (39 FR 38208). These regulations were issued under the authority of section 18 of the Noise Control Act of 1972, which also directed the Secretary of Transportation to promulgate regulations to ensure compliance with the EPA standards.

On February 28, 1975, the Federal Highway Administration (FHWA) published in the Federal Register (40 FR 8658) a text of proposed regulations establishing measurement methodologies for determining whether commercial motor vehicles (CMV) conform to the Interstate Motor Carrier Noise Emission Standards published by the EPA at 40 CFR part 202. FHWA published final regulations on September 12, 1975 (40 FR 42432). The new requirements, found at 29 CFR 325.91, became effective on October 15, 1975.

The current requirements of § 325.91—unchanged since their adoption in 1975—were established to support enforcement of EPA's Interstate Motor Carrier Noise Emission Standards. While the corresponding section of the EPA regulation requires CMVs with a GVWR or GCWR of more than 10,000 pounds which are operated by interstate motor carriers to be “ * * * equipped with a muffler or other noise dissipative device; * * *”, the language adopted by FHWA in § 325.91 requires the same vehicles to be “ * * * equipped with either a muffler or other noise dissipative device, such as a turbocharger (supercharger driven by exhaust gases) * * *.”

It is not clear why the language that was adopted in § 325.91 is largely identical to that established by EPA except that it additionally considers a turbocharger to be a noise dissipative device under § 325.91(b). There is no discussion in the preambles to either the February 1975 notice of proposed rulemaking or in the September 1975 final rule explaining why turbochargers were specifically included in the list of noise dissipative devices. In its petition, the Truck Manufacturers Association (TMA) noted:

At the time these regulations were written, many diesel engines were naturally aspirated, and coincidently much louder than then-comparable turbocharged equipped engines/trucks. In that context, it made sense to include turbochargers with mufflers as acceptable noise dissipative devices, since both devices quieted trucks appreciably compared to trucks with naturally aspirated engines and totally unmuffled exhaust systems.

All newly manufactured trucks are currently equipped and certified to meet EPA's Transportation Equipment Noise Emission Controls requirement of 80 dB(A) (40 CFR part 205) when they are placed into initial service. Section 325.91 provides a simple inspection protocol to assist Federal and State safety inspectors in confirming compliance with the EPA exhaust system requirements of the Interstate Motor Carrier Noise Emission Standards (40 CFR 202.22).

While FMCSA believes that the vast majority of CMV operators currently comply with § 325.91, the TMA petition notes that the regulatory language of § 325.91, as currently written, conceivably permits vehicle operators to remove mufflers or other noise dissipative devices and still meet the Federal inspection requirements merely because the CMV engine is equipped with a turbocharger.

In its petition, TMA noted that

* * * removing the muffler can cause the truck to be 10-20 dB(A) louder; a 10 to 100 fold increase in the emitted sound power level of the vehicle.

Additionally, TMA stated that it is * * * not aware of any other credible, satisfactorily performing, and commercially available exhaust noise dissipative device other than mufflers.

Petition for Rulemaking

In its June 17, 2005 petition for rulemaking, TMA requested that the Federal Motor Carrier Safety Regulations (FMCSRs) be amended to eliminate turbochargers from the list of equipment considered to be noise dissipative devices. TMA proposes that the phrase “, such as a turbocharger (supercharger driven by exhaust gases)” be removed from 49 CFR 325.91(b).

Request for Comments

FMCSA requests public comment on TMA's petition for rulemaking to amend 49 CFR 325.91(b). Specifically, FMCSA requests that commenters indicate whether they believe the FMCSRs should be amended as requested by the petitioner and whether there is any data or other relevant information to suggest the need for such a change. FMCSA also requests information concerning the impact of the requested change on motor carriers' ability to achieve compliance with the requirements of section 325.91.

FMCSA will consider all comments received by close of business on October 25, 2006. Comments will be available for examination in the docket at the location listed under the ADDRESSES section of this notice. FMCSA will file comments received after the comment closing date in the public docket and will consider them to the extent practicable. In addition to late comments, FMCSA will also continue to file in the public docket relevant information that becomes available after the comment closing date. Interested persons should monitor the public docket for new material.

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Issued on: September 8, 2006.

John H. Hill,


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[FR Doc. 06-8156 Filed 9-22-06; 8:45 am]