The FHWA published in a final rule on June 13, 1994, a list of weight restrictions for the interstate system and length restrictions for the NN (Tables 2A – English units and 2B – metric units). If the height and load of your low-loader are slightly above the legal limits, consider buying or renting a low-deck trailer. A drop-down deck trailer can be less than 2 feet tall, while a standard flatbed truck is 5 feet. With this difference, larger shipments have ample additional customs clearance, which can prevent additional permits. Semi-trailers of a maximum length which were actually and lawfully circulating in a tractor of a State on 1 December 1982 may continue to circulate after that date. In order to clarify what these lengths were for each state, “grandfathered” semi-trailer lengths were established by regulation (Table 1). The transport of bulky goods requires several considerations, one of the most important being the maximum height of the trailer. If you want to buy or lease a commercial trailer, you need to know all the details about the type of trailer that best suits your cargo to make sure you make the right choice. If no semi-trailer is attached to tow hitch B, the combination is included in the length measurement of the first semi-trailer and the length of 14.63 m (48 feet) or grandfathered applies. If you are a driver, you always know where to find the height of your trailer. Trailer heights are clearly marked on the edge of the trailers, allowing the driver to easily see the height when approaching potentially dangerous bridges. Federal length restrictions are primarily minimum requirements that states must allow for subsequent vehicles on the NN and appropriate access lanes.
While the overall range for trailer height is between 13 feet 6 inches and 14 feet, many states have exceptions. Some allow a higher cargo, others shorter depending on the type of route. A camel is a box, bridge or plate mounted behind the cab and in front of the fifth wheel coupling on the engine frame of a tractor to transport goods (Figures 13 and 14). Semi-trailer tractors so equipped on 1 December 1982 shall, during their useful life, be subject to the same national length requirements as any other combination of tractors and semi-trailers. The burden of proof of this legal effect on 1 December 1982 lies with the operator of the installation. The STAA approved the creation of a “national network” for trucks, where federal width and length restrictions would apply. It includes the interstate system and other designated highways, which opened Sept. 1.
In June 1991, the primary system of federal assistance was part of the primary system of federal assistance. The NN now covers more than 321,890 kilometers (km) (200,000 miles) of highways across the country. Non-interstate NN highways are listed in 23 CFR Part 658, Schedule A. Most highway bridges have a sign that tells drivers the height, but some bridges may have a unique shape that affects that height at the edges. As seen in the photo above, the median deck clearance provides generous space for most trailers, but the edges are well below the average height of 13 feet 6 inches. Devices excluded from length measurement include: (1) devices necessary for loading or unloading which do not extend more than 24 inches beyond the rear of the vehicle; (2) elastic bumpers that do not extend more than 6 inches beyond the front or rear of the vehicles; (3) aerodynamic devices that do not exceed more than 5 feet beyond the rear of the vehicle, provided they do not have the force, stiffness or mass necessary to damage a vehicle or injure a passenger in a vehicle striking a trailer so equipped from behind and do not obscure the taillights or turn signals, the necessary position lamps, identification lights or other safety devices; such as dangerous goods signs or conspicuous markings; and (4) non-proprietary equipment that does not extend more than 3 inches beyond the rear of the vehicle. All devices at the front of a semi-trailer or trailer are excluded from the length measurement. Buoyancy systems for open trailers or semi-trailers are excluded, provided that no part of the system is more than 3 inches from the sides or rear of the vehicle.
For more details on these exclusions, see 23 CFR 658.16 and Appendix D through 23 CFR 658. All states have their legal height restrictions. This is a combined or total height of the trailer and load. A 5` low loader can carry an 8`6″ piece, giving a total height of 13`6″. If the example was 14 feet in total, you could legally move to the western states, but the eastern states would need a permit for excess height. Although more specialized trailers like a Double Drop can pull larger loads, they have the same limits of limiting the total height. A “B train” is a tractor-trailer combination. In this combination, the two castors are connected by a fifth wheel attached to a chassis under the first semi-trailer that protrudes from the rear of this semi-trailer (the so-called “B-train” coupling).
The second semi-trailer connects to the first semi-trailer to this fifth wheel coupling (fig. 9). B-train combinations are subject to the same length restrictions (65 feet) as truck-tractor-trailer-trailer combinations. Figure 3. Truck-tractor-trailer combination States shall grant commercial vehicles that do not exceed the maximum width and minimum length limits applicable to the NN (excluding combinations subject to the ISTEA longitude stop) adequate access between the NN and terminals and facilities for periods of food, fuel, repair and rest.
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