What Are the Maximum Legal Length, Width, Height, and Weight Limits Allowed on Roads, Highways, or Interstates?

The legal maximum length, width, height, and weight permitted to travel, tow, or transport on local roads, highways, or Interstates in the United States and Canada are as follows.

These rules pertain to single personal vehicles (towed or otherwise) and commercial motor vehicles, including semi-tractors, trailers, and buses. Mirrors and certain safety devices (such as flags, etc.) may be permitted to protrude a “reasonable” distance further. Always obtain official consultation about any protrusion(s) you may have by contacting your state/provincial DOT office before any movement. Local city/county roads may vary from the maximum length, width, height, or weight limits governed by federal guidelines.

Exceptions:

Within Hawaii, commercial motor vehicles are permitted the following maximum width on all highways (unless otherwise posted on the road by sign): Standard: 9 feet or 108 inches. Metric: 2.74 meters or 274 centimeters.

These roads usually have signs posted that display the maximum legal width permitted without obtaining a special travel permit. You should always inquire about the maximum widths permitted by the governing body of the particular road before traveling on it to prevent a fine or worse. Depending on the width of the vehicle or shipment size, a route survey will be required before being granted permission to travel.

The Importance of Setting Maximum Widths for Vehicles

Safety and protection of motorists and public property are the primary reasons regulations have been set for maximum vehicle length, width, height, and weight limitations.

A standard was required based on the dimensions of the existing roads that would protect any/all persons operating a motor vehicle on highways, roads, and Interstates. Note that the public property is also at risk for damage. If motorists accidentally hit one of the many obstructions, such as guard rails, signs, traffic signal poles, etc., it’s their liability. However,  if not reported, the state is required to repair damages passed to taxpayers in both the USA and Canada. Therefore, maximum widths were created to protect human lives and public property.

Noteworthy information:

“Federal width limits don’t apply to special mobile equipment, which consists of self-propelled vehicles not designed or used primarily to transport persons or property and only incidentally moved over the highways. Special mobile equipment includes the following when moving under their power:

• military or farm equipment
• instruments of husbandry
• road construction or maintenance machinery
• emergency apparatus, including police and fire emergency equipment. 

Federal rules do not require States to issue overwidth permits before allowing the operation of special mobile equipment. However, if States wish to allow other vehicles more than 102 inches wide (i.e., non-special mobile equipment) to operate on the NN, then States must issue special overwidth permits.” Reference Credit: FHWA website.

History of Maximum Dimensions and Weight on Roads

“The Federal Government first enacted size regulations for CMVs with the passage of the Federal-Aid Highway Act of 1956. This Act provided a maximum vehicle width of 96 inches (2.44 meters) on the Interstate highway system. Subsequently, the Federal-Aid Highway Act of 1976 increased the allowable width for buses to 102 inches (2.6 meters). Finally, the Surface Transportation Assistance Act (STAA) of 1982 extended the same width requirement of 102 inches to commercial trucks. At the same time, the STAA expanded the highway network on which the Federal width provision applied from the Interstate to the National Network (NN) of highways.” Reference Credit: FHWA website.

Related links:

See regulations for maximum load limitations.
Learn what a route survey is.
Maximum legal load sizes.
Multi-state and regional permits.