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Bridge Formula Weights

Federal Bridge Formula

Explaining the maximum weight any combined set of axles on a truck and trailer can carry to cross a bridge on the Interstate highway system.  The following formula is used for calculating acceptable weights:

W=500 [ LN/N-1 + 12N + 36]

W= the overall gross weight on any group of two or more consecutive axles the the nearest 500 pounds.

L= the distance in feet between the outer axles of any group of two or more consecutive axles.

N= the number of axles in the group that are under consideration.

Axle spacing is another consideration that must be taken into account when looking at the Federal weight compliance laws.  In order to properly protect our bridges the number and the spacing of truck and trailer axles carrying the shipment must be calculated.  So a bridge weight formula applies when the gross weight on 2 or more consecutive axles exceeds the limitations on the formula, except that the 2 consecutive sets of tandem axles may carry a gross weight load of 34,000 pounds each if the overall distance between the 1st and last axle is  over a 36′ minimum.

There are exceptions.  Federal law does include an exception to the Federal Bridge Formula and the bridge table. 2 consecutive sets of tandem axles may carry 34,000 pounds each IF the overall distance between the first axle and last axles of these tandems is 36′ or greater.  For example:  a 5 axle tractor semi trailer combination may carry 34,000 pounds of weight both on the tractor tandem (axles 2 and 3) and the trailer tandem (axles 4 and 5), provided the axles 2 and 5 are spaced at least 36′ from each other.  Without this exception the bridge formula would allow for actual weight of only 66,000 pounds to 67,000 pounds on tandems spaced 36′ to 38′ apart. (References: U. S. Department of TransportationFederal Highway AdministrationFederal Bridge Formula Weights“)

Note:  In addition to the above formula weights Federal law says that a single axle is limited to a maximum of no greater than 20,000 pounds and that axles that are closer than 96″ from each other are limited to a maximum weight of 34,000 pounds.  Also that gross vehicle weight be less than 80,000 pounds

    Exceptions to the Bridge Weight Formula

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

2018 Federal Bridge Weight Chart

2
axles
3
axles
4
axles
5
axles
6
axles
7
axles
8
axles
9
axles
Less than 8’3″ 34,000 34,000
More than 8’4″ 38,000 42,000
9 39,000 42,500
10 40,000 43,500
11 44,000
12 45,000 50,000
13 45,000 50,500
14 46,500 51,500
15 47,000 52,000
16 48,000 52,500 58,000
17 48,500 53,500 58,500
18 49,500 54,000 59,000
19 50,500 54,500 60,000
20 51,000 55,500 60,500 66,000
21 51,500 56,000 61,000 66,500
22 52,500 56,500 61,500 67,000
23 53,000 57,500 62,500 68,000
24 54,000 58,000 63,000 68,500 74,000
25 54,500 58,500 63,500 69,000 74,500
26 55,500 59,500 64,000 69,500 75,000
27 56,000 60,000 65,000 70,000 75,500
28 57,000 60,500 65,500 71,000 76,500 82,000
29 57,500 61,500 66,000 71,500 77,000 82,500
30 58,500 62,000 66,500 72,000 77,500 83,000
31

59,000 62,500 67,500 72,500 78,000 83,500
32 60,000 63,500 68,000 73,000 78,500 84,500 90,000
33 64,000 68,500 74,000 79,000 85,000 90,500
34 64,500 69,000 74,500 80,000 85,500 91,000
35 65,500 70,000 75,000 80,500 86,000 91,500
36 66,000 70,500 75,500 81,000 86,500 92,000
37 66,500 71,000 76,000 81,500 87,000 93,000
38 67,500 71,500 77,000 82,000 87,500 93,500
39 68,000 72,500 77,500 83,500 88,500 94,000
40 68,500 73,000 78,000 84,000 89,000 94,500
41 69,500 73,500 78,500 84,500 89,500 95,000
42 70,000 74,000 79,000 84,500 90,000 95,500
43 70,500 75,000 80,000 85,000 90,500 96,000
44 71,500 75,500 80,500 85,500 91,000 96,500
45 72,000 76,000 81,000 86,000 91,500 97,500
46 72,500 76,500 81,500 87,000 92,500 98,000
47 73,500 77,500 82,000 87,500 93,000 98,500
48 74,000 78,000 83,000 88,000 93,500 99,000
49 74,500 78,500 83,500 88,500 94,000 99,500
50 75,500 79,000 84,000 89,000 94,500 100,000
51 76,000 80,000 84,500 89,500 95,000 100,500
52 76,500 80,500 85,000 90,500 95,500 101,000
53 77,500 81,000 86,000 91,000 96,500 101,500
54 78,000 81,500 86,500 91,500 97,000 102,000
55 78,500 82,500 87,000 92,000 97,500 102,500
56 79,500 83,000 87,500 92,500 98,000 103,000
57 80,000 83,500 88,000 93,000 98,500 104,000
58

84,000 89,000 94,000 99,000 104,500
59

85,000 89,500 94,500 99,500 105,000
60

85,500 90,000 95,000 100,500 105,500

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