In 1975, the U.S. Congress enacted the bridge formula to limit the weight-length ratio of a vehicle crossing a bridge. This is done by increasing the distance between axels or by spreading weight over additional axles. The reason for the formula is because, during the 1950s and 1960s, trucks grew heavier and began putting too much strain on bridges on the interstate highways.
The bridge formula is calculated by multiplying the distance in feet between the outer axles of any group of two or more consecutive axles by the number of axles in the group under consideration. This number is then divided by the number of axles in the group under consideration minus one. After getting this quotient, add 36 and the product of 12 times the number of axles in the group under consideration to the quotient. This final number is then multiplied by 500 to get the overall gross weight on any group of two or more consecutive axles to the nearest 500 pounds.
In addition to the bridge formula weight limits, federal law states that gross weight vehicle is limit to 80,000 pounds.
States have given exemptions to different types of vehicles to operate above the standard federal truck size and weight limits. This exemption often only applies to non-Interstate highways.
Below is each state’s maximum gross weight limit. Each state’s interstate limit is 80,000 lbs. unless exempt or indicated that longer combination vehicles (LCV) are exempt.
Bridge Weight Limit (lbs)
Bridge Axle Limit
Bridge Weight Limit Exemption