Load Type: 
Divisible Non-divisible

THE BRIDGE FORMULA

W=500[LN/N-1+12N+36]
W
The maximum weight in pounds that can be carried on a group of two or more axles to the nearest 500 pounds
 L
The distance in feet between the outer axles of any two or more consecutive axles
 N
The number of axles in a group

WHY THE FORMULA IS NECESSARY
Bridges on interstate system highways are used by a wide variety of traffic. They are designed to support expected loadings. However, as trucks grew heavier in the 1950s and 1960s, something had to be done to protect bridges. The solution was to tie allowable weights to the number and spacing of axles.

Axle spacing is as important as axle weight in bridge design. A bridge is analogous to thin ice on a pond. Walking on the ice concentrates a person's weight on the small area covered by the individual's feet, and then the ice may break. Lying down, however, spreads the same weight over a much larger area, and the ice is less likely to break.

In 1982, Federal law was amended to make interstate systems weight limits, including the bridge formula limits, both the maximum and the minimum weights (i.e., floors and ceilings) that states must allow on the interstate system.

HOW TO USE THIS CALCULATOR

1
 First select load type
2
 Then enter the axle group spacing and axle width information. You may also enter the amount of weight you'd like to transport.
3
 When all information for your vehicle is entered, click "Add axle group" for more axles, or or click "Calculate."
4
 If there are any axle groups or bridges over weight, you may enter new information and re-calculate.
5
 Click the printer icon to print the page when you're finished.