23 C.F.R. § 658 app D to Part 658
The following devices are excluded from measurement of the length or width of a commercial motor vehicle, as long as they do not carry property and do not exceed the dimensional limitations included in § 658.16 . This list is not exhaustive.
1. All devices at the front of a semitrailer or trailer including, but not limited to, the following:
(a) A device at the front of a trailer chassis to secure containers and prevent movement in transit;
(b) A front coupler device on a semitrailer or trailer used in road and rail intermodal operations;
(c) Aerodynamic devices, air deflector;
(d) Air compressor;
(e) Certificate holder (manifest box);
(f) Door vent hardware;
(g) Electrical connector;
(h) Gladhand;
(i) Handhold;
(j) Hazardous materials placards and holders;
(k) Heater;
(l) Ladder;
(m) Non-load carrying tie-down devices on automobile transporters;
(n) Pickup plate lip;
(o) Pump offline on tank trailer;
(p) Refrigeration unit;
(q) Removable bulkhead;
(r) Removable stakes;
(s) Stabilizing jack (anti-nosedive device);
(t) Stake pockets;
(u) Step;
(v) Tarp basket;
(w) Tire carrier; and
(x) Uppercoupler.
2. Devices excluded from length measurement at the rear of a semitrailer or trailer including, but not limited to, the following:
(a) Handhold;
(b) Hazardous materials placards and holders;
(c) Ladder;
(d) Pintle hook;
(e) Removable stakes;
(f) Splash and spray suppression device;
(g) Stake pockets; and
(h) Step.
3. Devices excluded from width determination, not to exceed 3 inches from the side of the vehicle including, but not limited to, the following:
(a) Corner caps;
(b) Hazardous materials placards and holders;
(c) Lift pads for trailer on flatcar (piggyback) operation;
(d) Rain gutters;
(e) Rear and side door hinges and their protective hardware;
(f) Side marker lamps;
(g) Structural reinforcement for side doors or intermodal operation (limited to 1 inch from the side within the 3 inch maximum extension);
(h) Tarping systems for open-top trailers;
(i) Movable devices to enclose the cargo area of flatbed semitrailers or trailers, usually called tarping systems, where no component part of the system extends more than 3 inches from the sides or back of the vehicle when the vehicle is in operation. This exclusion applies to all component parts of tarping systems, including the transverse structure at the front of the vehicle to which the sliding walls and roof of the tarp mechanism are attached, provided the structure is not also intended or designed to comply with 49 CFR 393.106 , which requires a headerboard strong enough to prevent cargo from penetrating or crushing the cab; the transverse structure may be up to 108 inches wide if properly centered so that neither side extends more than 3 inches beyond the structural edge of the vehicle. Also excluded from measurement are side rails running the length of the vehicle and rear doors, provided the only function of the latter, like that of the transverse structure at the front of the vehicle, is to seal the cargo area and anchor the sliding walls and roof. On the other hand, a headerboard designed to comply with 49 CFR 393.106 is load bearing and thus limited to 102 inches in width. However, the "wings" designed to close the gap between such a headerboard and the movable walls and roof of a tarping system are width exclusive, provided they are add-on pieces designed to bear only the load of the tarping system itself and are not integral parts of the load-bearing headerboard structure;
(j) Tie-down assembly on platform trailers;
(k) Wall variation from true flat; and
(l) Weevil pins and sockets on low-bed trailers.
23 C.F.R. § 658 app D to Part 658