Truck and trailer rules in Idaho: licence classes, trailer brakes, size and weight limits and the chip truck chain exemption

This page reports what the official source says. It is not legal advice: ask the office named here. All of the sources are sections of Idaho Code Title 49, Motor Vehicles, published by the Idaho Legislature: the definitions in chapter 1, the equipment rules in chapter 9 and the weight, speed and tire rules in chapter 10. Federal background and the other places are on the parent page, trucks and trailers for tree work.

At a glance

Item	What the sources say
Commercial motor vehicle	Combination rating over 26,000 pounds including a towed unit rated over 10,000 pounds; or a single vehicle rated over 26,000 pounds
Class A	Combination rated over 26,000 pounds when the towed vehicle is rated over 10,000 pounds
Class B	Single vehicle rated over 26,000 pounds, or one towing a vehicle rated 10,000 pounds or less
Trailer brakes	Required on a trailer or semitrailer of 1,500 pounds unladen weight or more; automatic on breakaway
Width, height	8 1/2 feet wide; 14 feet high
Length	45 feet single motor vehicle; 48 feet trailer or semitrailer; 75 feet for a motor vehicle with one or more trailers
Gross weight	20,000 pounds single axle; 105,500 pounds vehicle or combination, 80,000 pounds on interstate highways
Safety chain	Not published on the pages read
Carrier number	Not published on the pages read

Licence classes

Section 49-123 defines a commercial motor vehicle for the driver licence and equipment chapters as a vehicle or combination used to carry passengers or property that has a manufacturer's gross combination weight rating over 26,000 pounds including a towed unit rated over 10,000 pounds, or a gross vehicle weight rating over 26,000 pounds. A vehicle built for 16 or more people and any size of vehicle that carries placarded hazardous materials also count. Section 49-105 then sets the classes. Class A covers a combination rated over 26,000 pounds when the vehicle towed is rated over 10,000 pounds. Class B covers a single vehicle rated over 26,000 pounds, or such a vehicle towing a vehicle rated not over 10,000 pounds. Class C covers a vehicle or combination that is not class A or B but carries 16 or more people or placarded hazardous materials. A double or triple trailer needs endorsement T on a class A, B or C licence. See section 49-105 on definitions and licence classes.

Brakes and the chip truck chain exemption

Section 49-933 says every trailer or semitrailer of an unladen weight of 1,500 pounds or more must have brakes adequate to control, stop and hold the vehicle, designed to be applied by the driver of the towing vehicle from the cab. The brakes must be connected so that they apply automatically in an accidental breakaway of the towed vehicle. A trailer or semitrailer under 1,500 pounds unladen need not have brakes, and a farm trailer used within 50 miles hauling farm products is exempt. For stopping, a combination with a gross vehicle weight rating of 10,000 pounds or more is held to a 50 foot stop from 20 miles per hour and 43.5 percent braking force. See section 49-933 on brakes.

Section 49-948 deals with tires and with chains on mountain passes. If the Idaho Transportation Department finds that Lookout Pass, Fourth of July Pass or Lolo Pass is unsafe without chains, it may set a chain requirement for commercial vehicles on interstate 90 or state highway 12. The requirement is met by chaining one tire on each side of one drive axle and one axle near the rear of each towed vehicle. The exempt list in subsection 9 includes motor carriers that transport forest products at any time of the year, and names chip trucks. The section also bars studded tires on public highways between May 1 and September 30, with exceptions.

Size and weight

Section 49-1010 sets a width of 8 1/2 feet and a height of 14 feet, with equipment the board finds necessary for safe operation left out of width and length. Length limits are 45 feet for a single motor vehicle, 48 feet for a trailer or semitrailer, 75 feet for a motor vehicle with one or more trailers, and no more than three units in a combination except for a saddlemount combination. A load may not extend more than 4 feet past the front or 10 feet past the end of a vehicle. Section 49-1001 caps the single axle at 20,000 pounds, a single wheel at 10,000 pounds and a vehicle or combination at 105,500 pounds, with 80,000 pounds on federal interstate and defense highways unless a permit applies. Section 49-1011 lets vehicles that transport forest products run up to 2,000 pounds over an axle, bridge or gross limit on highways outside the interstate system. See section 49-1010 on size of vehicles and loads.