General Knowledge: Weights And Dimensions
9 questions in the bank cover this topic. Everything below is drawn from the sources those questions cite.
Sources: 23 CFR 658.15, 23 CFR 658.17
What you need to know
658.17(b) sets 80,000 pounds as the ceiling, but the bridge formula can require less depending on how your axles are spaced.
Legal weight is never just a number on a scale ticket; it depends on where that weight sits.
The maximum gross vehicle weight shall be 80,000 pounds except where lower gross vehicle weight is dictated by the bridge formula.
23 CFR 658.17
658.17(c) sets 20,000 pounds on any one axle, including a single axle within a group.
You can be legal on gross weight and still illegal on one axle, which is what sliding a fifth wheel or a tandem is for. None of the figures offered is the one the rule gives.
The maximum gross weight upon any one axle, including any one axle of a group of axles, or a vehicle is 20,000 pounds.
23 CFR 658.17
658.17(d) sets 34,000 pounds for a tandem, which is less than twice the 20,000 pound single axle limit.
Two axles close together concentrate load on the same stretch of bridge deck.
The maximum gross weight on tandem axles is 34,000 pounds.
23 CFR 658.17
658.17(e) applies the formula to the gross weight carried on any two or more consecutive axles, not to the vehicle as a whole.
It is why axle SPACING changes what you may legally carry: the same 80,000 pounds spread over a longer wheelbase puts less load on any one bridge span.
No vehicle or combination of vehicles shall be moved or operated on any Interstate highway when the gross weight on two or more consecutive axles exceeds the limitations prescribed by the following formula, referred to as the Bridge Gross Weight Formula:
23 CFR 658.17
658.17(f) prevents states from setting tire load limits below 500 pounds per inch of width, and excludes steering axle tires from such limits entirely.
Such limits may not be applied to steering axle tires at all. None of the figures offered is the one the rule gives.
States may not limit tire loads to less than 500 pounds per inch of tire or tread width, except that such limits may not be applied to tires on the steering axle.
23 CFR 658.17
658.17(f) stops a state setting an unworkably low steering axle limit.
The manufacturer's rating governs where it is the lower of the two, because no regulation can make an axle carry more than it was built for.
States may not limit steering axle weights to less than 20,000 pounds or the axle rating established by the manufacturer, whichever is lower.
23 CFR 658.17
658.17(g) makes the limits all-inclusive.
The only allowance is a scale factor for portable wheel-load weighers, capped at 5 percent. A penalty schedule that fines nothing up to 1,000 pounds counts as an unauthorised tolerance.
The weights in paragraphs (b), (c), (d), and (e) of this section shall be inclusive of all tolerances, enforcement or otherwise
23 CFR 658.17
658.15(a) fixes it at 102 inches, and notably states may impose neither more nor less.
Hawaii keeps a 108-inch maximum by statute. Special use permits can still be granted for wider loads.
No State shall impose a width limitation of more or less than 102 inches, or its approximate metric equivalent, 2.6 meters (102.36 inches) on a vehicle operating on the National Network
23 CFR 658.15
658.17(h) allows special permits for NONDIVISIBLE loads, meaning ones that cannot be broken down without compromising their value or use.
A load you could simply split into two trips does not qualify.
States may issue special permits without regard to the axle, gross, or Federal Bridge Formula requirements for nondivisible vehicles or loads.
23 CFR 658.17
Check yourself
- What is the maximum gross vehicle weight for an Interstate run?
- The maximum weight on any single axle is ______.
- The maximum weight on a tandem axle set is ______.
- What is limited by the Bridge Gross Weight Formula?
- What is the tire load floor a state must respect?
- What two figures set the floor for a state steering axle limit?
- Do the federal weight limits include an enforcement tolerance?
- What width applies on the National Network?
- When may a state permit your load exceeding the federal axle, gross and bridge formula limits?
Answers are in the practice test for this topic.