Part 393 specifies the required color, position, and types of lamps and reflectors for commercial motor vehicles. All lamps and reflectors for commercial motor vehicles manufactured after March 7, 1989 must meet the requirements of Federal Motor Vehicle Safety Standard (FMVSS) No. 108 (49 CFR 571.108) in effect on the date of manufacture. Certain trailers manufactured on or after December 1, 1993, must have retro-reflective sheeting or additional reflex reflectors to make them more visible to other motorists under conditions of reduced visibility. Lamps and reflectors on commercial motor vehicles manufactured on or prior to March 7, 1989 must meet either the requirements of Part 393 or of FMVSS No. 108 that were in effect on the date of manufacture.
Must be operable All required lamps must light on request at an inspection and must light when required during regular operation of the vehicle.
Lamp mounting All lamps must be permanently and securely mounted on a permanent part of the vehicle. The exceptions are temporary lamps, such as those used in a driveaway-towaway operation or mounted on projecting loads. Temporary lamps must be securely attached.
Stop lamps All stop lamps on a commercial motor vehicle must activate when the service brakes are applied.

A service brake system that meets the requirements of 49 CFR 393.52, which specifies braking and holding performance.

A parking brake system that meets the requirements of 49 CFR 393.41, which specifies parking brake activation and the method for holding the brakes in the applied position.

An emergency brake system that conforms to the requirements of 49 CFR 393.52 and consists of either (1) emergency features of the service brake system or (2) a system separate from the service brake system. See Section 393.40--Required brake systems.

Trucks and truck tractors with three or more axles, manufactured before July 25, 1980, are not required to have steering axle brakes.

Any full trailer, semitrailer, or pole trailer having a gross weight of 3,000 pounds or less, provided the trailer weight does not exceed 40 percent of weight of the towing vehicle.

&127; Every truck or truck tractor equipped with air brakes, when used to tow other vehicles equipped with air brakes, must be capable of activating (manually and automatically) the emergency features of the trailer brakes. The brakes must apply automatically when the towing vehicle air supply pressure is between 20 and 45 psi. The manual control must be operable by the driver from the driver’s seat, with seat belt in use.

&127; Every trailer is required to be equipped with brakes that apply automatically if the trailer breaks away from the towing vehicle*. The brakes must remain in the applied position for at least 15 minutes.
*These requirements do not apply to vehicles in driveaway-towaway operations

Safe and reliable operation of a vehicle’s brakes depends upon adequate protection of the tubing and hoses from mechanical and other damage.Design and construction of brake tubing and hose must ensure proper, adequate, and continued functioning. Installation must ensure proper functioning of the hose. Length and flexibility must accommodate all normal motions of the parts to which the hose is attached. Protection against mechanical damage must include protection against chafing, kinking, and mechanical damage. Protection from high temperature must include protection from or location away from exhaust pipes and other sources of high temperatures.

Each fuel system must be located so that no part of the system extends beyond the widest part of the vehicle, no part of a fuel tank is forward of the front axle or a power unit. In addition, fuel lines may not extend between a towed vehicle and the towing unit while the combination is in motion.

• Body ply or belt material exposed through the tread or sidewall
• Tread or sidewall separation
• Audible leak (or flat)
• A cut exposing the ply or belt material
• A tread groove pattern depth of less than 4/32 of an inch (front tires) or 2/32 of an inch (other tires)
• Regrooved tires on front wheels of trucks or truck tractors which have a load carrying
• capacity equal to or greater than 8.25-20 8-ply rating tires
• Regrooved, recapped, or retreaded tires on the front wheels of buses are prohibited.

Sleeper berths must meet minimum dimensions. A sleeper berth must not be installed on a trailer and must be located in or adjacent to the cab. An exit door at least 18" high by 36" wide must lead directly into the cab. Section 393.76 contains special provisions for sleeper berths installed before 1975.

Sleeper berths must be equipped with adequate sheets and blankets, and a mattress and springs or innerspring mattress. They must be adequately ventilated, and located so as to protect occupants against exhaust heat and fumes and fuel leaks. A mandatory restraint system must withstand at least 6,000 lbs. of force applied toward the front of the vehicle.

Exhaust systems must meet the following requirements:

The exhaust system and discharge must be located where it is not likely to burn or damage the electrical wiring, the fuel supply, nor any combustible part of the vehicle. The discharge from the exhaust system must not be located immediately below the fuel tank or the fuel tank filler pipe. The exhaust system may not be temporarily repaired with patch or wrap material.

The exhaust pipe and mufflers must be securely fastened to the vehicle. The exhaust system may not leak or discharge at any point forward of or directly below the driver or sleeper compartment. For trucks and truck tractors, the exhaust system must discharge at a location to the rear of the cab, or above and near the rear of the cab.

For a bus powered by a gasoline engine, the exhaust pipe must discharge at a point no farther forward than six inches forward of the rearmost part of the bus. For a bus powered by diesel or other fuel (not gasoline), the exhaust pipe must discharge either At a point no farther forward than 15 inches forward of the rearmost part of the bus, or To the rear of all doors or windows designed to be open (not including emergency exits).

One extinguisher with a UL rating of 5 B:C or more or Two extinguishers each with a UL rating of 4 B:C or more.

One extinguisher with a UL rating of 10 B:C, if the vehicle is transporting placardable quantities of hazardous material.

Steering wheel must be properly secured and no cracked or missing spokes. Steering wheel lash must meet the requirements of Section 393.209. Steering column must be securely fastened. Steering system must not have worn or welded universal joints, loose steering gear box, missing bolts, or a loose pitman arm on the steering gear output shaft. Power steering unit must not have loose or broken parts, frayed, cracked, or slipping belts; leaks; or insufficient fluid in reservoir.