# Federal Motor Vehicle Safety Standards; Air Brake Systems; Air Compressor Cut-In
> **National Highway Traffic Safety Administration** · Final rule. · Published 1996-02-16 · 61 FR 6173
## Document
- **Document number:** 96-3258
- **Category:** fmvss
- **Sub-agency:** National Highway Traffic Safety Administration
- **Federal Register citation:** 61 FR 6173
- **CFR reference:** 49 CFR 571
- **Publication date:** 1996-02-16
- **DOT docket:** Docket No. 90-3
## Abstract

This document concludes a rulemaking proceeding begun in response to a petition for rulemaking submitted by the Truck Trailer Manufacturers Association (TTMA). It amends Standard No. 121, Air Brake Systems, to require the automatic activation of the air compressor on a powered vehicle whenever the pressure in the air brake system drops below 100 pounds per square inch (psi). The agency has concluded that the amendment will ensure that new truck tractors provide trailers with sufficient air pressure for release of the trailer parking brakes and provide adequate service braking. In addition, the amendment will provide greater air reserves on all air braked vehicles.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/1996/02/16/96-3258/federal-motor-vehicle-safety-standards-air-brake-systems-air-compressor-cut-in)
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