Truck Driver's Guidebook
Bridge Gross Weight Formula
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The Bridge Gross Weight Formula was developed to prevent stress to highway bridges caused by heavy trucks. The formula provides a standard to control the spacing of truck axles and weight on those axles. Vehicles with a gross weight of 80,000 pounds or less may be eligible for increased weights using the Bridge Gross Weight Formula. Vehicles exceeding a gross weight of 80,000 pounds or the gross weight calculated using the Bridge Weight Formula are not eligible for bridge weights (exception: 5 axle tandem tandems).  

The Bridge Gross Weight Formula allows:

• 20,000 pounds for a single axle
• 34,000 pounds for a tandem axle group

The weight of other axle groups would be determined using the Bridge Gross Weight 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 spacing in feet between the outer axles of any two or more consecutive axles

N = The number of axles being considered

A Bridge Gross Weight Formula chart is provided on the back inside cover of the Truck Driver's Guidebook. The chart is an easy means of determining permissible gross loads for vehicles in regular operation. To order a guidebook, you can either call (800) 682-4682, or click here.

When using the formula chart:

                        

                      

Measure the axle group spacing

                        

(This is the maximum allowable gross vehicle weight for the group. All groups must be legal.)
 

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Due to frequent changes in federal and state regulations, the Michigan Center for Truck Safety cannot ensure the accuracy of the material contained in the Guidebook beyond the date of publication. For current information, contact the Center at (800) 682-4682. This document is not intended for legal purposes.