What is the maximum width on highways, roads and interstates?

What is the maximum width allowed on Interstates and highways (all reasonable access roads or what is referred to as the “National Network” or “NN”)? The maximum width allowed on Interstates and highways in North America is (unless otherwise posted by sign):

8 feet and 6 inches or 102.36 inches.

2.6 meters or 260 centimeters.

Within the state of Hawaii commercial motor vehicles are permitted the following maximum width on all highways (unless otherwise posted by sign):

9 feet or 108 inches.

2.74 meters or 274 centimeters.

Notes: These rules are for personal, commercial motor vehicles including semi tractors, trailers and buses. Mirrors and other items such as “mirrors” or “certain safety devices” (such as flags, etc.) are not included and may protrude out within a reasonable distance further. It should also be noted that there are county roads that do not support the maximum widths governed by federal guidelines. These roads usually have signs posted that display the maximum legal width permitted with out obtaining a special travel permit. You should always inquire about the maximum widths permitted by the governing body of the particular road prior to travelling on it in order to prevent a fine or worse. In some situations depending on the width of the vehicle or shipment size a route survey will be required prior to being granted permission to travel.

Maximum width allowed.

Maximum width laws are created to protect motorists and public assets. Know the maximums.

The importance of setting maximum widths for vehicles.

Safety of motorists and public property are the main reasons regulations were set for vehicle width maximums. 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. It should also be noted public property is placed at risk for damage as well. Should a motorists accidentally hit one of the many existing obstructions such as guard rails, signs, traffic signal poles, etc. liability while ultimately is the motorists, if it is not reported the state is required to repair damages which then is passed on to the taxpayers in both the USA and Canada. So maximum widths were created to protect both human lives but public property as well.

Maximum width allowed

Maximum vehicle width permitted on highways. Image credit FHWA.

Noteworthy information:

“Federal width limits do not apply to special mobile equipment, which consists of self-propelled vehicles not designed or used primarily for the transportation of persons or property and only incidentally moved over the highways. Special mobile equipment includes the following, when moving under their own power: military or farm equipment; instruments of husbandry; road construction or maintenance machinery; and emergency apparatus, including police and fire emergency equipment. Federal rules do not require States to issue overwidth permits before allowing 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.


“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). 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 length allowed on roads, highways and interstates.
Maximum legal load sizes.
Multi state and regional permits.



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