23 CFR 658.16 - Exclusions from length and width determinations.
(a) Vehicle components not excluded by law or regulation shall be included in the measurement of the length and width of commercial motor vehicles.
(b) The following shall be excluded from either the measured length or width of commercial motor vehicles, as applicable:
(1) Rear view mirrors, turn signal lamps, handholds for cab entry/egress, splash and spray suppressant devices, load induced tire bulge;
(2) All non-property-carrying devices, or components thereof -
(i) At the front of a semitrailer or trailer, or
(ii) That do not extend more than 3 inches beyond each side or the rear of the vehicle, or
(iii) That do not extend more than 24 inches beyond the rear of the vehicle and are needed for loading or unloading, or
(vi) Listed in appendix D to this part;
(3) Resilient bumpers that do not extend more than 6 inches beyond the front or rear of the vehicle;
(4) Aerodynamic devices that extend a maximum of 5 feet beyond the rear of the vehicle, provided such devices have neither the strength, rigidity nor mass to damage a vehicle, or injure a passenger in a vehicle, that strikes a trailer so equipped from the rear, and provided also that they do not obscure tail lamps, turn signals, marker lamps, identification lamps, or any other required safety devices, such as hazardous materials placards or conspicuity markings; and
(5) A fixed step up to 3 inches deep at the front of an existing automobile transporter until April 29, 2005. It will be the responsibility of the operator of the unit to prove that the step existed prior to April 29, 2002. Such proof can be in the form of a work order for equipment modification, a receipt for purchase and installation of the piece, or any similar type of documentation. However, after April 29, 2005, the step shall no longer be excluded from a vehicle's length.
(c) Each exclusion allowance is specific and may not be combined with other excluded devices.
(d) Measurements are to be made from a point on one side or end of a commercial motor vehicle to the same point on the opposite side or end of the vehicle.