Federal Bridge Law
Federal regulations limit vehicle size and weight on federal highways. This includes all interstate highways across the country, as well as other federal roads designated within the National Highway System or National Network.
Vehicle Weight Limits
Federal weight limits of vehicles and axle loading limits are governed by the Federal Bridge Law (FBL), which has four primary rules:
- The maximum weight allowed on a single axle is 20,000 lbs
- The maximum total weight allowed on any two consecutive axles spaced eight or fewer feet apart (like tandem axles) is 34,000 lbs
- The maximum allowed Gross Vehicle Weight (GVW), or the maximum allowed total weight on any group of consecutive axles on a vehicle, is determined by the Federal Bridge Formula (FBF).
- The maximum Gross Vehicle Weight (GVW) on Interstate highways is 80,000 lbs, even when the result of the formula is greater.
The Federal Bridge Formula (FBF)
W = [ ( (LN) / (N - 1) ) + 12N + 36 ]
- W = the maximum allowed total weight in pounds for all axles in the group (rounded to the nearest 500 lbs, and rounding down when right in the middle - i.e. 62,250 lbs rounds to 62,000, while 62,300 lbs rounds to 62,500)
- L = the length or distance in feet (rounded to the nearest foot) from the center of the forward-most axle in the group to the center of the rear-most axle in the group
- N = the total number of axles in the group
Essentially, the Federal Bridge Formula allows a vehicle to weigh more when there are more axles and/or there is more distance to spread its weight out.
The Federal Bridge TableFor convenience, the Federal Highway Administration published the Federal Bridge Table, which allows one to quickly lookup the federal maximum gross weight on a vehicle or group of consecutive axles, based on number of axles and overall axle length:
Federal Bridge Law Examples
Vehicle Size Limits
Federal regulations limit vehicle size as follows:
- Width: The maximum width of a vehicle is limited to 102 inches
- Length: For straight trucks*, vehicle length is not federally regulated. This regulation is left to the individual states.
- Height: Vehicle height is not federally regulated. This regulation is left to the individual states.
Colorado Bridge Laws
Notice: The Federal Bridge Law (FBL) applies to all interstate and federal highways across the nation. Additionally, the majority of states have adopted the Federal Bridge Formula (FBF) to some degree state-wide, in which case we may just refer to the "FBF" or "FBL". Expand the Federal Bridge Law panel above for the info on those federal regulations.
Colorado Vehicle Weight Limits
Quick Summary / Synopsis for Dump Trucks
On state and local roads, Colorado applies its own relatively simple bridge formula:
W = 1000 (L + 40)
Number of axles are spacing are not considered in the Colorado bridge formula. Like the FBL, individual axles are limited to 20,000 lbs, but Colorado treats tandem axles like two individual axles, and able to carry 40,000 lbs. Colorado's maximum GVW on non-Interstate roads is 85,000 lbs.
Colorado has an overweight permit that allows a truck having a quad axle grouping and a divisible load (like a dump truck) to carry 110,000 lbs as long as no axles exceed the 20,000 lb limit. The permit does NOT apply to Interstate highways.
The permit allows up to 110,000 lbs, but you need at least 6 axles to pull it off, due to the quad axle grouping requirement as well as the individual axle limit. So a quint axle (or Simple 16) dump truck can technically qualify, but it would need to properly distribute the weight to the axles to keep any axle from exceeding 20,000 lbs, which is unlikely. Due to the physics of the dump body located over the tandem drive axles, and pusher axles located between the front steer axle and the tandem drive axles, inevitably these trucks wind up with too much weight on the tandems, while efforts to reduce this weight with the pusher axles' loading result in too little weight on the front steer axle. A 6-axle Super Dump can pull off the weight distribution fairly easily however, because its trailing axle acts as a lever arm that shifts weight from the tandem axles to the front axle. Add in one more pusher axle, making it a 7-axle Super Dump, and weight distribution is even easier (the 3 pusher axles can be 13k pushers).
Want to forgo the overweight permit? Without the permit, you can run 81,000 lbs on a 5-axle Super Dump with a 318-inch wheelbase, by the Colorado bridge formula.
Examples for Colorado
Colorado Vehicle Size Limits
Colorado has the following restrictions on vehicle size*:
- Width: The maximum width of a vehicle is 102 inches
- Length: The maximum length of a straight truck is 45 feet
- Height: The maximum height of a vehicle is 14 feet 6 inches
We try to stay accurate and up-to-date with any changes to the state weight laws, specifically as they pertain to dump trucks, utilizing resources from the Federal Highway Association, popular national vehicle weight guides and manuals, and the individual states' government websites and their official statutes. The weight laws within individual states can be complicated, however, especially when special permits, federal law grandfather rights, seasonal stipulations, and so forth are thrown into the mix. Our purpose here is to present each state's weight laws as they pertain to the typical dump truck, doing typical dump truck work, in the most common dump truck circumstances. If you have some special circumstance or scenario with your truck, we encourage you to visit your state's government website directly, or call your state Department of Transportation. Additionally, if you've discovered an error with our presentation of your state's laws, please let us know via our Contact Us Form and we'll make any necessary corrections immediately.