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Regulatory Guidance

Welcome to the FMCSA Guidance Portal. This web portal is a searchable, indexed database that contains and links to all guidance documents in effect from the Federal Motor Carrier Safety Administration. The guidance documents lack the force and effect of law, unless expressly authorized by statute or incorporated into a contract.

To comment on any guidance document, or to request issuance, reconsideration, modification, or rescission of any guidance document, please identify the guidance document in your request and send it to: FMCSAguidance@dot.gov. NOTE: The FMCSAguidance mailbox is not intended to serve as a mailbox for general inquiries. For inquiries that go beyond the limited purpose of the FMCSAguidance mailbox, please call FMCSA's Information Line (800-832-5660) or visit FMCSA's "Contact Us" page to send your inquiry to the appropriate mailbox.

Subject Agency Identifier Topic Issued Date
If a CMV manufactured on or after July 25, 1980 (see § 393.42) has brake components on the front axle, and the brakes are not operable, does the vehicle comply with § 393.48? FMCSA-VEH-393.48-Q01 Is a post-1980 CMV with inoperable front brakes in compliance?
If a truck or truck tractor manufactured prior to July 25, 1980, and having 3 or more axles, has inoperable brakes on the front axle or some of the brake components are missing, would the vehicle be in violation of § 393.48? FMCSA-VEH-393.48-Q02 Is a pre-1980 CMV with inoperable front brakes in violation?
Are the brakes on a vehicle towed in a driveaway-towaway operation or towed disabled vehicle required to be operable at all times? FMCSA-VEH-393.48-Q03 Are operable brakes required on disabled or driveaway-towaway vehicles?
Is the low pressure warning device required to activate before the tractor protection valve? FMCSA-VEH-393.51-Q01 Must the low-pressure warning device activate before the tractor protection valve?
Is the vacuum portion of vacuum-assisted hydraulic brake systems required to have a warning device? FMCSA-VEH-393.51-Q02 Does vacuum assist on hydraulic brakes need a warning device?
Are vacuum gauges required on the vacuum portion of vacuum-assisted hydraulic brakes? FMCSA-VEH-393.51-Q03 Do vacuum-assisted hydraulic brake need a gauge on the vacuum portion?
Is a warning device required in a Commercial Motor Vehicle (CMV) with a single hydraulic brake system which uses the driveline parking brake as the emergency brake system? FMCSA-VEH-393.51-Q04 Is a warning device required on a hydraulic brake system with driveline parking brake as emergency brake?
What difference, if any, is there between a warning device and a warning signal? FMCSA-VEH-393.51-Q05 What’s the difference between a warning device and a warning signal?
May the information in the stopping distance table be used to determine the stopping distances at speeds greater than 20 mph? FMCSA-VEH-393.52-Q01 Can the stopping-distance table be used for speeds above 20 mph?
May windshields and side windows be tinted? FMCSA-VEH-393.60-Q01 Tinting of windshields and side windows