# Definitions.
**AGENCY:**
National Highway Traffic Safety Administration (NHTSA), Department of Transportation (DOT).
**ACTION:**
Correcting amendments.
**SUMMARY:**
This document contains corrections to the final rule regulations (49 CFR parts 523 and 535), which were published in the *Federal Register* of Thursday, September 15, 2011 (76 FR 57106). The regulations established fuel efficiency standards for medium- and heavy-duty engines and vehicles, as prescribed under the Energy Independence and Security Act (49 U.S.C. 32902(k)(2)).
**DATES:**
*Effective Date:* November 14, 2011.
**FOR FURTHER INFORMATION CONTACT:**
Lily Smith, Office of Chief Counsel, National Highway Traffic Safety Administration, 1200 New Jersey Avenue, SE., Washington, DC 20590. Telephone: (202) 366-2992.
**SUPPLEMENTARY INFORMATION:**
**Background**
NHTSA and EPA published in the *Federal Register* of September 15, 2011, final rules to establish a comprehensive Heavy-Duty National Program that will increase fuel efficiency and reduce greenhouse gas emissions for on-road heavy-duty vehicles, responding to the President's directive on May 21, 2010, to take coordinated steps to produce a new generation of clean heavy-duty vehicles.
**Need for Correction**
As published, the final regulations inadvertently inserted a new definition for “base tire” in 49 CFR part 523 instead of 49 CFR part 535. The new definition was intended to be applied to heavy-duty vehicles. It was not intended to replace the definition of “base tire” for light-duty vehicles, as its current location would suggest. To correct the mistake, NHTSA is moving the definition to its original intended location in 49 CFR part 535, and adding the words “for heavy-duty vehicles” to alleviate any confusion. The previous definition for “base tire” for light duty vehicles will be restored, and the words “for passenger automobiles, light trucks and medium-duty passenger vehicles” will be added.
**List of Subjects in 49 CFR Parts 523 and 535**
Fuel efficiency.
Accordingly, 49 CFR parts 523 and 535 are corrected by making the following correcting amendments:
**49 CFR Part 523**
**PART 523—VEHICLE CLASSIFICATION**
1. The authority citation for part 523 continues to read as follows:
**Authority:**
49 U.S.C. 32901, delegation of authority at 49 CFR 1.50.
**49 CFR Part 523**
2. In § 523.2, revise the definition of “Base tire” to read as follows:
§ 523.2
*Base tire* for passenger automobiles, light trucks and medium-duty passenger vehicles means the tire specified as standard equipment by a manufacturer on each vehicle configuration of a model type.
**49 CFR Part 535**
**PART 535—MEDIUM- AND HEAVY-DUTY VEHICLE FUEL EFFICIENCY PROGRAM**
3. The authority citation for part 535 continues to read as follows:
**Authority:**
49 U.S.C. 32902; delegation of authority at 49 CFR 1.50.
4. In § 535.4, add a definition of “Base tire” to read as follows:
§ 535.4
*Base tire* for heavy-duty vehicles means the tire specified as standard equipment by a manufacturer on each subconfiguration of a model type.
Issued: October 18, 2011.
Christopher J. Bonanti,
Associate Administrator for Rulemaking, National Highway Traffic Safety Administration, Department of Transportation.