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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
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
If a crack extended into the thickness of the glass at such an angle FMCSA-VEH-393.60-Q03 Definition of ¼” windshield crack
May a bus being operated by a for-hire motor carrier of passengers, under contract with a governmental agency to provide transportation of prisoners in interstate commerce, be allowed to operate with security bars covering the emergency push-out windows a FMCSA-VEH-393.62-Q01 May buses for prisoners block the emergency push-out windows?
When calculating the minimum emergency exit space required on school buses used in non-school bus operations, should two or three passengers per bench seat be used in determining the adult seating capacity? FMCSA-VEH-393.62-Q02 Seating capacity of school buses used for adults