A dump truck with a trailing axle in order to be federal bridge law compliant for larger weights

If you own a truck or a truck fleet, you must understand federal bridge laws. Nothing can stop a business in its tracks as quickly as a big fine for an overweight truck or a side-lined truck in your fleet.

Keep reading to learn how you can comply with federal bridge laws in all parts of the United States.

Federal Bridge Laws and Formulas

Federal Highway Administration and Federal Bridge Formula Weights determine the proper bridge weight formula, the weight a vehicle should be for a given bridge. The law states the amount of weight a vehicle may be depending on the number of axles and the distance between the axles.

This weight limit refers specifically to traveling on the Interstate highway system. So if you have trucks transporting heavy equipment on Interstate systems, you must understand the federal bridge laws.

To understand the bridge formula, you must first understand the terms.

  • W refers to the overall gross weight on any group of two or more consecutive axles to the nearest 500 pounds.
  • N refers to the number of axles in the group under consideration
  • L refers to the distance in feet between the outer axles of any group of two or more consecutive axles
  • the Federal Bridge Formula is thus W = 500 [ LN/N-1 + 12N + 36]

Here’s how to work your way through the formula to make sure you have the right weight. Begin with the inner part of the brackets.

  1. Multiply the number of axles times the distance in feet between the outer axles of any group of two or more consecutive axles.
  2. Then subtract one from the number of axles in the group under consideration.
  3. Divide your first number by your second number.
  4. Multiple 12 times N (the number of axles)
  5. Add that number to the number from step 3.
  6. Add 36 to the number you have from step 5.
  7. Multiply this final number times 500.

This final number is the maximum gross weight allowed. This means the truck and its load may not weigh more than this final number.

How The Federal Bridge Formula Works

You need to understand three basic definitions to understand the Bridge Formula.

  1. Gross Weight: This number refers to the weight of the vehicle and its load. You may not have a vehicle with more than an 80,000-pound gross weight unless the Bridge Formula makes the weight limit lower.
  2. Single-Axle Weight: This weight number refers to the total weight on single axles not spaced more than 40 inches apart from other axles. You may not legally have more than 20,000 pounds on a single axle when traveling on the Interstate System.
  3. Tandem-Axle Weight: This refers to the total weight on consecutive axles with centers spaced between 41 and 96 inches apart. On the Interstate System, the Federal government limits your tandem-axle weight to 34,000 pounds.

The history of truck production helps best explain the Bridge formula. Post World War II, truck manufacturers began to produce heavier trucks. As a result, the federal government became concerned about the wear and tear on bridges.

Thus, the federal government adopted axle and gross weight limits on the Interstate System in 1956. Some states were allowed to “grandfather” or keep higher weight limits.

The number of axles and the distance between axles help create a formula that protects bridges and keeps trucks and drivers safer when driving on aging infrastructure.

For example, a single-axle weight limit takes the place of the Bridge Formula weight limit on axles that are less than 40 inches apart. The tandem-axle weight limit takes the place of the Bridge Formula weight limit when the axles are between 40 and 96 inches apart.

So when you have two axles that are 97 inches apart, the truck may carry 38,000 pounds.

State Specific Laws

Each state has its own weight-limit statutes as well. These have clauses which include a level of restriction on state weight limits. This way states can still receive Federal funds because they’re complying with Federal requirements.

If a state were to not follow the Federal provisions, they run the risk of losing essential Federal funds for not complying.

States comply in a few different ways. Many pay close attention to Federal law changes. Then they require their legislature or their State Department to raise limits when the Federal law changes. The states may also require the legislature or State Department to increase the weight limits if their current laws do not comply with Federal law.

Most states have two different weight limits. They have one for State highways and another for Interstate highways. Often the weight-limit laws do not state the specific limits for Interstates in the statute, though, because the Federal law makes that clear.

In Connecticut, Nebraska, Hawaii, Nevada, New York, New Jersey, Wyoming, and Washington, the weight limit in the law is actually higher than the Federal Limits for Interstate travel. However, the statutes have a Federal compliance clause. This clause protects states from losing Federal funding by stating that Federal weight limits still apply to the Interstate system.

Research the state where you plan on trucking to learn its specific requirements. You are responsible for knowing and following the laws where you travel and work.

Best Practices

Ultimately, truck owners and fleet owners must make sure their trucks comply with the laws of the states they visit. You can ensure compliance by making sure your weight does not exceed the limitations of the state or the federal formula.

Measure your axles. Know your truck dimensions. Do not fib on the weight of the truck.

Then make sure you’re keeping your truck in good working order. If you’re not sure about specifics for truck inspection, hire a professional service for your truck inspection.

Federal bridge laws exist to protect roads, bridges, and the trucks that travel on them. If you know the law and follow it, you have nothing to worry about. If you skip a step and try to guess the weight of your truck, you’ll end up with a hefty fine and a sidelined truck.

As you can see, there are many factors involved in choosing the right equipment while staying compliant with federal and state laws. We have product specialists ready to assist you in finding the right products and options for your needs. Contact us to get started!