Truck and trailer rules in Missouri: commercial licence line, 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. All of the sources are sections of the Revised Statutes of Missouri, published on the Missouri Revisor of Statutes website. 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	Gross vehicle weight rating or weight of 26,001 pounds or more; or a combination of 26,001 pounds or more that includes a towed unit rated over 10,000 pounds
Brakes	Two sets of adequate brakes on every motor vehicle except a motorcycle; no trailer weight line in the section read
Safety chain	Required on a towed vehicle in addition to the primary coupling, with listed exceptions
Width, height	102 inches wide; 14 feet high on the interstate and designated routes, 13 1/2 feet on other highways
Length	45 feet single motor vehicle; 65 feet for most other combinations on primary and interstate highways, 55 feet on other highways
Gross weight	80,000 pounds, with 20,000 pounds on one axle and 34,000 pounds on a tandem axle
Loose loads	Goods that could fall off must be covered or secured; a violation is a class C misdemeanor
Carrier registration	The Highways and Transportation Commission administers Unified Carrier Registration for Missouri-domiciled carriers

The commercial vehicle line

The Uniform Commercial Driver's License Act, sections 302.700 to 302.780, defines a commercial motor vehicle as a motor vehicle or combination used in commerce to carry passengers or property. It meets the definition in four ways. The first is a gross combination weight rating or weight of 26,001 pounds or more, whichever is greater, where the combination includes a towed unit with a gross vehicle weight rating or weight of more than 10,000 pounds. The second is a gross vehicle weight rating or weight of 26,001 pounds or more. The third is a vehicle designed to carry 16 or more passengers including the driver. The fourth is a vehicle carrying hazardous materials that must be placarded. The same section defines a commercial driver's license as one issued under 49 CFR part 383, and a commercial learner's permit as the permit that allows behind-the-wheel training with a licence holder. The section was in effect from August 28, 2018. See section 302.700 on the commercial driver's licence definitions.

Brakes, safety chains and projecting loads

Section 307.170 covers other equipment on motor vehicles and has been in effect since August 28, 1996. Subsection 3 says all motor vehicles except motorcycles must always have two sets of adequate brakes in good working order. The section read does not name a trailer weight at which separate trailer brakes begin.

Subsection 6 says that when one vehicle tows another, the connecting device may not exceed 15 feet. Every towed vehicle must be coupled to the towing vehicle by a safety chain, cable or equivalent device in addition to the primary coupling. The secondary device must be strong enough to control the towed vehicle if the primary coupling fails. The secondary device is not needed where the connecting device is attached to the towing vehicle by a center-locking ball located over or nearly over the rear axle and not carried by the rear bumper. Subsection 7 leaves out farm implements and any vehicle that does not have to be registered.

Subsection 5 says a vehicle carrying poles or other objects that project more than five feet past the rear must carry a red light at the end of the object while lights are required. At other times it must show a red flag or cloth not less than 16 inches square. Subsection 8 says commercial motor vehicles and trailers on a state highway must have adequate and proper brakes, lighting, signalling devices, steering, horns, mirrors, wipers, tires, wheels, exhaust, glazing, fuel tank and other safety equipment, in a condition to obtain the certificate of inspection under section 307.360. A violation is an infraction. See section 307.170 on other vehicle equipment.

Loads that could come off

Section 307.010, in effect from August 28, 2025, covers goods and material on a motor vehicle, trailer or semitrailer that could reasonably be expected to become dislodged and fall because of wind or air pressure or the movement of the vehicle. Such a load must have a protective cover or be secured so no part can fall off while it is carried. The section lists ways a cotton trailer can comply, and says operating in violation is a class C misdemeanor. See section 307.010 on securing loads.

Width, height and length

Section 304.170, in effect from August 28, 2020, says no vehicle may have a width, including load, over 102 inches, apart from clearance lights, mirrors and accessories required by law. Height, including load, may not exceed 14 feet on the interstate system or any route designated by the commission, and 13 1/2 feet on all other highways. A single motor vehicle may not exceed 45 feet in length including load. A truck-tractor and semitrailer may not exceed 60 feet, and the section caps the semitrailer at 53 feet. A truck-tractor with a semitrailer and a trailer is held to 65 feet on the primary highways not designated by the commission. Any other combination may not exceed 65 feet on primary or interstate highways, plus a distance of ten miles from them, or 55 feet on any other highway. Farm implements and some other movements are left out of the restrictions. See section 304.170 on width, height and length.

Weight

Section 304.180, in effect from August 28, 2023, says no vehicle or combination may be moved on a highway with more than 20,000 pounds on one axle or more than 34,000 pounds on a tandem axle. A tandem axle is a group of two or more axles more than 40 inches and not more than 96 inches apart between the extremes. Groups of consecutive axles follow a table of maximum loads by the distance between the extremes of the group. Total gross weight may not exceed 80,000 pounds, except as the section provides for listed cases. See section 304.180 on weight.

Carrier registration

Section 390.021, in effect from August 28, 2008, says the state highways and transportation commission may run the state's part of the Unified Carrier Registration plan. It administers the registration of Missouri-domiciled motor carriers, motor private carriers, brokers, freight forwarders and leasing companies, and collects the registration fees. The section read does not give a fee table or a weight line for a tree-service truck. See section 390.021 on Unified Carrier Registration.