Exception to Formula and Table B

Federal law (23 U.S.C. 127) includes one exception to the Bridge Formula and Table B—two consecutive sets of tandem axles may carry 34,000 lbs. each if the overall distance between the first and last axles of these tandems is 36 feet or more. For example, a five-axle tractor-semitrailer combination may carry 34,000 lbs. both on the tractor tandem (axles 2 and 3) and the trailer tandem (axles 4 and 5), provided axles 2 and 5 are spaced at least 36 feet apart. Without this exception, the Bridge Formula would allow an actual weight of only 66,000 and 67,500 lbs. on tandems spaced 36 to 38 feet apart.

Bridge Formula Application to Single Unit Trucks

The procedure described above can be used to check any axle combinations, but several closely spaced axles usually produce the most critical situation.

The truck in Figure 8 satisfies the single axle weight limit (12,000 lbs. is less than 20,000 lbs.), the tandem axle limit (30,000 lbs. is less than 34,000 lbs.) and gross weight limit (57,000 lbs. is less than 80,000 lbs.). With these restrictions satisfied, a check will be made for Bridge Formula requirements, axles 1 through 4.

Actual weight = 12,000 + 15,000 + 15,000 + 15,000 = 57,000 lbs.
W maximum for "N" of 4 and "L" of 23 feet = 57,500 (From Table B).
Since axles 1 thru 4 are satisfactory, check axles 2 thru 4:
W (actual) = 15,000 + 15,000 + 15,000 = 45,000 lbs.
W maximum for "N" of 3 and "L" of 9 feet = 42,500 lbs. (From Table B).

Caution This pamphlet paraphrases the actual provisions in 23 U.S.C. 127 and 23 CFR 658 for the sake of clarity. In case of a dispute, the statute and regulations will govern. Previous editions of this pamphlet released under the title "Bridge Gross Weight Formula," dated April 1984, remain valid. Neither the Formula nor any resulting maximum gross weight values (table entries) have been changed.