The weight on various axle configurations must be checked to determine compliance with the Bridge Formula. To correct the situation, some load must be removed from the vehicle or the axle spacing (35 feet) must be increased.

ops.fhwa.dot.gov. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. Thus, the Bridge Formula requirement is satisfied. This is a violation because the actual weight exceeds the weight allowed by the Bridge Formula.

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Bridges on the Interstate System highways are designed to support a wide variety of vehicles and their expected loads. stream

Figure 3 shows the most common vehicle checked for compliance with weight limit requirements. It is important to note that the single-axle weight limit replaces the Bridge Formula weight limit on axles not more than 40 inches apart, and the tandem-axle weight limit replaces the Bridge Formula weight limit for axles over 40 but not more than 96 inches apart. Maximum weight (W) = 80,000 pounds (Bridge Table for "L" of 51 feet and "N" of 5 axles). Maximum weight (W) = 57,500 pounds (Bridge Table for "L" of 23 feet and "N" of 4 axles). When the Interstate System axle and gross weight limits were adopted in 1956, and amended in 1975, States were allowed to keep or "grandfather" weight limits that were higher. L = the distance in feet between the outer axles of any group of two or more consecutive axles. The solution was to link allowable weights to the number and spacing of axles. 127). In Figure 1A, the stress on bridge members as a longer truck rolls across is much less than that caused by a short vehicle as shown in Figure 1B, even though both trucks have the same total weight and individual axle weights. Maximum weight (W) = 65,500 pounds (Bridge Table for "L" of 35 feet and "N" of 4 axles). With these restrictions satisfied, a check is done for Bridge Formula requirements, axles 1 through 4. Maximum weight (W) = 51,000 pounds, which is more than the actual weight of 46,000 pounds. This is a violation because the actual weight exceeds the weight allowed by the Bridge Formula.

Bridge Formula calculations yield a series of weights (Bridge Table, pages 5-6). Thus, these preliminary requirements are satisfied. Office of Operations The truck shown in Figure 8 satisfies the single-axle weight limit (12,000 pounds are less than 20,000 pounds), the tandem-axle limit (30,000 pounds are less than 34,000 pounds) and the gross-weight limit (57,000 pounds are less than 80,000 pounds). x]Ys9~WtXUGjYX=PH+! Three definitions are needed to use the Bridge Formula correctly. 658 for purposes of illustration only. Federal law states that any two or more consecutive axles may not exceed the weight computed by the Bridge Formula even though single axles, tandem axles, and gross weight are within legal limits. In addition to the grandfather rights notes on page 3, Federal law (23 U.S.C. <> Maximum weight (W) = 42,500 pounds (Bridge Table for "L" of 9 feet and "N" of 3 axles. As trucks grew heavier in the 1950s and 1960, something had to be done to protect bridges. At 97 inches apart, for example, two axles may carry 38,000 pounds (Figure 2A) and three axles may carry 42,000 pounds, as shown in Figure 2B. <> The load must either be reduced, axles added, or spacing increased to comply with the Bridge Formula. This same number (51,000 pounds) could have been obtained from the Bridge Table by reading down the left side to L = 20 and across to the right where N = 3. Federal Highway Administration You may need the Adobe Reader to view the PDFs on this page. Before checking for compliance with the Bridge Formula, a vehicle's single-axle, tandem-axle, and gross weight should be checked. endobj 3 0 obj As a result, the axle group that includes the entire trucksometimes called the "outer bridge" groupmust comply with the Bridge Formula. Interstate System weight limits in some States may be higher than the figures noted above due to "grandfather" rights. In addition to Bridge Formula weight limits, Federal law states that single axles are limited to 20,000 pounds, and axles spaced more than 40 inches and not more than 96 inches apart (tandem axles) are limited to 34,000 pounds. Permissible Gross Loads for Vehicles in Regular Operation1. This is accomplished either by spreading weight over additional axles or by increasing the distance between axles. With a few exceptions noted in this pamphlet, the Bridge Formula establishes the maximum weight any set of axles on a motor vehicle may carry on the Interstate highway system. Actual weight = 17,000 + 17,000 + 17,000 + 17,000 = 68,000 pounds. % <>/ExtGState<>/XObject<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/Annots[ 25 0 R 28 0 R 31 0 R 34 0 R] /MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> In the event of a dispute, the statute and regulation take precedence with respect to maximum allowable Federal Bridge Formula weights. %PDF-1.5 The first Bridge Formula combination is checked as follows: Actual weight = 12,000 + 17,000 + 17,000 = 46,000 pounds. 2 0 obj endobj For example, a five-axle tractor-semitrailer combination may carry 34,000 pounds 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. Washington, DC 20590 <>>> Although the Bridge Formula applies to each combination of two or more axles, experience shows that axle combinations 1 through 3, 1 through 5, and 2 through 5 are critical and must be checked. The weight of the longer vehicle is spread out, while the shorter vehicle is concentrated on a smaller area. Therefore, this axle spacing is satisfactory. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement. The Federal Highway Administration (FHWA) revises its guidance pamphlet Federal Bridge Formula Weights (May 2015). Axle spacing is as important as axle weight in designing bridges. If these combinations are found to be satisfactory, then all of the others on this type of vehicle normally will be satisfactory. 127 and 23 C.F.R. Actual weight = 12,000 + 15,000 + 15,000 + 15,000 = 57,000 pounds. Privacy Policy, United States Department of Transportation - Federal Highway Administration, Permissible Gross Loads for Vehicles in Regular Operation. This guidance paraphrases provisions of 23 U.S.C. Actual weight = 12,000 + 17,000 + 17,000 + 17,000 + 17,000 = 80,000 pounds. 1200 New Jersey Avenue, SE 4 0 obj