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  • § 393.11
    Lamps and reflective devices.
  • § 393.17
    Lamps and reflectors—combinations in driveaway-towaway operation.
  • § 393.24
    Requirements for head lamps, auxiliary driving lamps and front fog lamps.
  • § 393.25
    Requirements for lamps other than head lamps.
  • § 393.28
    Wiring systems.
  • § 393.40
    Required brake systems.
  • § 393.41
    Parking brake system.
  • § 393.42
    Brakes required on all wheels.
  • § 393.43
    Breakaway and emergency braking.
  • § 393.44
    Front brake lines, protection.
  • § 393.48
    Brakes to be operative.
  • § 393.51
    Warning signals, air pressure and vacuum gauges.
  • § 393.52
    Brake performance.
  • § 393.60
    Glazing in specified openings.
  • § 393.61
    Truck and truck tractor window construction.
  • § 393.62
    Emergency exits for buses.
  • § 393.65
    All fuel systems.
  • § 393.67
    Liquid fuel tanks.
  • § 393.70
    Coupling devices and towing methods, except for driveaway-towaway operations.
  • § 393.71
    Coupling devices and towing methods, driveaway-towaway operations.
  • § 393.75
  • § 393.76
    Sleeper berths.
  • § 393.81
  • § 393.82
  • § 393.83
    Exhaust systems.
  • § 393.87
    Warning flags on projecting loads.
  • § 393.88
    Television receivers.
  • § 393.89
    Buses, driveshaft protection.
  • § 393.92
  • § 393.93
    Seats, seat belt assemblies, and seat belt assembly anchorages.
  • § 393.100
    Which types of commercial motor vehicles are subject to the cargo securement standards of this subpart, and what general requirements apply?
  • § 393.102
    What are the minimum performance criteria for cargo securement devices and systems?
  • § 393.106
    What are the general requirements for securing articles of cargo?
  • § 393.201

Part 393

Section § 393.70: Coupling devices and towing methods, except for driveaway-towaway operations.

Below are the available interpretations for the given section. To return to the list of parts, use the Parts link above. The menu to the left provides a full list of sections that have interpretations. To view interpretations for a different section, click on the menu item.

The regulations text of the section can be found on the eCFR website. To view the regulations text, use the link below. For assistance, please send an email to
View regulations for Part 393

Question 1: Is there a minimum number of fasteners required to fasten the upper fifth wheel plate to the frame of a trailer?

Guidance: The Federal Motor Carrier Safety Regulations (FMCSRs) do not specify a minimum number of fasteners. However, the industry recommends that a minimum of ten 5/8 inch bolts be used. If ½ inch bolts are used, the industry recommends at least 14 bolts. The Commercial Vehicle Safety Alliance (CVSA) has adopted these industry standards as a part of its vehicle out-of-service criteria.

Question 2: When two safety chains are used, must the ultimate combined breaking strength of each chain be equal to the gross weight of the towed vehicle(s) or would the requirements be met if the combined breaking strength of the two chains is equal to the gross weight of the towed vehicle(s)?

Guidance: If the ultimate combined breaking strength of the two chains is equal to the gross weight of the towed vehicle(s), the requirements of §393.70(d) are satisfied. It should be noted that some States may have more stringent requirements for safety chains.

Question 3: §393.70(d) requires that every full trailer must be coupled to the frame, or an extension of the frame, of the motor vehicle which tows it with one or more safety devices to prevent the towed vehicle from breaking loose in the event the tow-bar fails or becomes disconnected. The safety device must be connected to the towed and towing vehicles and to the tow-bar in a manner which prevents the tow-bar from dropping to the ground in the event it fails or becomes disconnected. Would the use of a pair of safety chains/cables between the towing vehicle and the front of a fixed-length draw bar, or an extendible draw bar, with a separate pair of safety chains/cables between the end of the draw bar and the front of the towed vehicle meet the requirements of §393.70(d)?


Generally, separate safety devices at the front and rear of the draw bar could be used to satisfy the requirements of §393.70(d) provided the safety devices are attached to the draw-bar and the vehicles in a manner that prevents the drawbar from dropping to the ground in the event that it fails or becomes disconnected. Also, the arrangement of the safety device(s) must be such that the vehicles will not separate if the draw bar fails or becomes disconnected.

If the drawbar design is such that bolts, connecting pins, etc., are used to connect structural members of the drawbar, and are located at or near the midpoint of the drawbar (beyond the attachment points for the safety chain at the ends of the draw bar) the safety devices would have to extend from either the frame of the towed or towing vehicle to a point beyond the bolts, connecting pins or similar devices.

In the case of an extendible draw bar or reach, if a separate safety device(s) is used for the front and rear of the drawbar, a means must be provided to ensure that the draw bar will not separate at the movable portion of the drawbar. The use of welded tube stops would satisfy the intent of §393.70(d) if the ultimate strength of the welds exceeds the impact forces associated with the drawbar extending suddenly with a fully loaded trailer attached.

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