Vehicle Size and Weight Limits
What this domain tests
This domain asks about legal size and weight limits and how they interact. It covers gross weight, axle weight, bridge formula, width, height, and permit loads.
Core rules
- Common federal limits are 80,000 pounds gross vehicle weight, 20,000 pounds on a single axle, and 34,000 pounds on a tandem axle.
- Common legal dimensions are 8 feet 6 inches wide and 13 feet 6 inches high. Longer combination vehicles may need permits.
- The bridge formula limits how much weight can be carried over a given distance between axles. A legal gross weight can still violate the bridge formula or an axle limit.
- Oversize or overweight loads require permits, and permit routes may exclude some roads and bridges.
Worked example
A combination scales 12,000 pounds on the steer axle, 34,000 on the first tandem, and 34,000 on the second tandem. The gross is 80,000 pounds and the tandem axles are legal, but the steer axle must also be checked against its tire and axle rating.
Traps
Checking only gross weight, ignoring tire ratings, and assuming a permit covers every road are common misses.