Motor Carrier Bridge Allowance

Figure Bridge Allowance

Truck image to figure Bridge Allowance

BRIDGE FORMULA

Axle weights and maximum gross weight for combinations registered in Classes 21 through 25 (greater than 73,280 pounds) and carrying more than 73,280 pounds are determined by the Bridge Formula.

NOTE:
The Bridge Formula also applies to out-of-state combinations registered or authorized to carry and carrying more than 73,280 pounds.

INSTRUCTIONS FOR DETERMINING BRIDGE FORMULA


FIRST STEP: Measure the external bridge of the combination, the center-to-center distance between the first and last axles. With this distance, you can determine the maximum allowable gross weight of the combination. Example: Using the illustration as an example, the external bridge measures 50 feet. Using the Bridge Formula Table - Table 2, locate 50 feet in the left-hand column. Follow the 50 feet line to the column title "5 axles." The table shows that 79,500 pounds is the maximum gross weight, which may be carried on the entire five-axle combination.

SECOND STEP: Measure the internal bridge of the combination, the center-to-center distance between the second and last axles. With this distance, you can determine the maximum allowable gross weight on this group of axles.
Example: Again using the illustration, the internal bridge measures 36 feet. Using the Bridge Formula Table - Table 2; locate 36 feet in the left-hand column. Follow the 36 feet line to the column title "4 axles." The table shows that 68,000 pounds is the maximum allowable gross weight, which may be carried on the four-axle group.
The Bridge Formula Law further specifies that the overall gross weight on any group of two or more consecutive axles can't exceed that produced by using the Bridge Formula. (For example, two axles on a four-foot spacing are permitted to carry 34,000 pounds for the pair according to the Bridge Formula table.) The law also allows two consecutive pairs of axles to carry up to 34,000 pounds each, if the overall distance between the first and last axles of the consecutive pairs is at least 36 feet.

With the Bridge Formula Law applying to any group of two or more consecutive axles, experience shows that axle groups two and three, four and five, two through five (internal bridge) and one through five (external bridge) are the critical groups that should always be checked.

In most cases, depending on the type of load carried and only 8,000 to 9,000 pounds is carried on the steering axle. Therefore, care must be taken in determining overall gross weight using the Bridge Formula. The recommended method is to determine the overall gross weight allowed on the internal bridge and add the known amount actually carried on the steering axle. Example: Using the illustration allowing 68,000 pounds on the internal bridge (36 feet - four axles) and assuming 8,000 pounds actually carried on the steering axle, the maximum gross weight which may be legally carried is 76,000 pounds. This method may also be used to determine the maximum gross weight at which a combination should be registered.

Under the Bridge Formula, no individual axle may exceed 20,000 pounds.

Table 2 - BRIDGE FORMULA TABLE

Center to center distance in feet Between the first and last axles of an Maximum load in pounds carried on any Group of 2 or more consecutive axles group of 2 or more consecutive axles 2 axles 3 axles 4 axles 5 axles 6 axles 7 axles

4 = 34,000
5 = 5,000
6 = 36,000
7 = 37,000
8 = 38,000-42,000
9 = 39,000 - 43,000
10 = 40,000 43,500
11 = 44,500
12 = 45,000 - 50,000
13 = 46,000 - 50,500
14 = 46,500 - 51,500
15 = 47,500 - 52,000
16 = 48,000 - 52,500 - 58,000
17 = 49,000 - 53,500 - 58,500
18 = 49,500 - 54,000 - 59,500
19 = 50,500 - 54,500 - 60,000
20 = 51,000 - 55,500 - 60,500 - 65,000
21 = 52,000 - 56,000 - 61,000 - 66,000
22 = 52,500 - 56,500 - 62,000 - 67,000
23 = 53,500 - 57,500 - 62,500 - 68,000
24 = 54,000 - 58,000 - 63,000 - 68,500 - 74,000
25 = 55,000 - 58,500 - 63,500 - 69,000 - 74,500
26 = 55,500 - 59,500 - 64,500 - 69,500 - 75,000
27 = 56,500 - 60,000 - 65,000 - 70,000 - 76,000
28 = 57,000 - 60,500 - 65,500 - 71,000 - 76,500
29 = 58,000 6- 1,500 - 66,000 - 71,500 - 77,000
30 = 58,500 - 62,000 - 67,000 - 72,000 - 77,500
31 = 59,500 - 62,500 - 67,500 - 72,500 - 78,000
32 = 60,000 - 63,500 - 68,000 - 73,000 - 78,500
33 = 64,000 - 68,500 74,000 79,500
34 = 64,500 - 69,500 - 74,500 - 80,000
35 = 65,500 70,000 75,000 80,000
36 = 68,000 - 70,500 - 75,500 - 80,000
37 = 68,000 - 71,000 - 76,000 - 80,000
38 = 68,000 - 72,000 - 77,000 - 80,000
39 = 68,000 - 72,500 - 77,500 - 80,000
40 = 68,500 - 73,000 - 78,000 - 80,000
41 = 69,500 - 73,500 - 78,500 - 80,000
42 = 70,000 - 74,500 - 79,000 - 80,000
43 = 70,500 - 75,000 - 80,000 - 80,000
44 = 71,500 - 75,500 - 80,000 - 80,000
45 = 72,000 - 76,000 - 80,000 - 80,000
46 = 77,000 - 80,000 - 80,000
47 = 77,500 - 80,000 - 80,000
48 = 78,000 - 80,000 - 80,000
49 = 78,500 - 80,000- 80,000
50 = 79,500 - 80,000 - 80,000
51 & more = 80,000 - 80,000 80,000