Truck and trailer rules in Colorado: licence classes, trailer brakes, safety chains, size and weight limits

This page reports what the official source says. It is not legal advice: ask the office named here. The sources are the Colorado Revised Statutes 2024, Title 42, Vehicles and Traffic, as printed by the Colorado General Assembly (the printout is marked uncertified), the Colorado Division of Motor Vehicles commercial driver license page and the Colorado Department of Transportation permitting page. Federal background and the other places are on the parent page, trucks and trailers for tree work.

At a glance

The commercial vehicle line and licence classes

Section 42-2-402 defines a commercial motor vehicle as a motor vehicle designed or used to carry passengers or property that has a gross vehicle weight rating of 26,001 pounds or more or a lesser rating set by federal regulation, is designed to carry 16 or more passengers including the driver, or carries hazardous materials that must be placarded under 49 CFR part 172, subpart F. The definition leaves out recreational vehicles, military vehicles driven by military personnel and certain farm vehicles run by a farmer. The Colorado DMV commercial driver license page lists the classes. Class A is any combination with a gross combination weight rating of 26,001 pounds or more where the towed vehicle is rated over 10,000 pounds. Class B is any single vehicle rated 26,001 pounds or more, or one towing a vehicle not rated over 10,000 pounds. Class C is a single vehicle or combination that is neither, but carries 16 or more passengers including the driver or is placarded for hazardous materials. The same page says Colorado does not issue non-domiciled commercial licences or learner permits, a suspension it dates September 29, 2025.

Brakes and safety chains

Section 42-4-223 requires every motor vehicle other than a motorcycle to have brakes adequate to control, stop and hold it, with two separate means of applying them, each effective on at least two wheels. Every trailer or semitrailer of a gross weight of 3,000 pounds or more must have brakes adequate to control, stop and hold it, designed to be applied by the driver of the towing vehicle from the cab, and connected so that on an accidental breakaway the brakes apply automatically. Such a trailer must have brakes on all wheels. The section excludes some farm trailers and fertilizer tank and distributor trailers of up to 10,000 pounds gross, and a trailer under 3,000 pounds gross need not have brakes. Service brakes must stop a vehicle or combination from 20 miles per hour within 40 feet on dry level pavement, and the hand brake within 55 feet.

Section 42-4-506 says that when one vehicle tows another, the drawbar or other connection must be strong enough to pull all weight towed and may not exceed 15 feet between vehicles, with exceptions for poles, pipe, machinery and other structural objects that cannot readily be taken apart. A chain, rope or cable connection must show a white flag or cloth of not less than 12 inches square. Safety chains or cables are required as well, arranged so the towed vehicle cannot break loose if the connection fails, except where a fifth wheel connection meets the department's requirements.

Width, height and length

Section 42-4-502 limits the total outside width of a vehicle or its load to 8 feet 6 inches, with listed exceptions such as hay loads and recreational vehicle appurtenances up to 9 feet 6 inches overall. Clearance lights, rearview mirrors and accessories required by law may project beyond that width. Section 42-4-504 bars driving a vehicle, unladen or with load, over 14 feet 6 inches, and tells the Department of Transportation to designate highways with structures lower than that. No single motor vehicle may exceed 45 feet extreme overall length including bumpers. A combination may consist of no more than four units and may not exceed 70 feet overall, a limit that does not apply to unladen truck tractor and semitrailer combinations with a semitrailer of 57 feet 4 inches or less. A load may not project more than four feet beyond the grille at the front, and the section sets no more than ten feet at the rear for steel, beams, trusses, utility poles and pipes. The Colorado Department of Transportation permitting page gives the same height, width and weight figures in plain words and points to extra-legal permits for loads beyond them.

Weight

Section 42-4-507 limits the gross weight on a wheel with a pneumatic tire to 9,000 pounds and on a single axle with pneumatic tires to 20,000 pounds. The single axle figure is 21,000 pounds for a digger derrick or bucket boom truck run by an electric utility on a highway outside the interstate system. A tandem axle with pneumatic tires may carry 36,000 pounds on the interstate and 40,000 pounds elsewhere. A single axle means all wheels whose centres lie between two vertical planes not more than 40 inches apart. Section 42-4-508 caps gross weight by the formula W = 1,000 (L + 40), with L the distance in feet between the centres of the first and last axles, and states that the figure must not exceed 85,000 pounds. On the interstate a separate formula applies, capped at 80,000 pounds. A vehicle in a combination may not carry less than ten percent of the combination's gross weight, with an exception for specialized pole trailers and fixed public utility trailers. The Department of Transportation page gives the legal weight as 80,000 pounds on the interstate and 85,000 pounds on non-interstate highways.

Sources

• Colorado General Assembly, Colorado Revised Statutes 2024 Title 42 Vehicles and Traffic (sections 42-2-402, 42-4-223, 42-4-502, 42-4-504, 42-4-506 to 42-4-508; uncertified printout), read October 9, 2026
• Colorado Department of Revenue, Division of Motor Vehicles, commercial driver license general information, read October 9, 2026
• Colorado Department of Transportation, Freight and Permitting, permitting information, read October 9, 2026