Montana CDL Truck Rules: Size, Weight, Chains and Traction Devices

A Montana CDL does not just license you to drive a truck. It puts you on long stretches of two-lane highway, over mountain terrain and through a winter that can close a road without much warning. Montana's truck rules are mostly about size, weight and winter equipment, and the numbers below come from the state's own trucker materials and the Montana Motor Vehicle Division (MVD).

What size limits apply to Montana trucks?

• Width: 102 inches.
• Height: 14 feet without a permit.
• Single power unit: 55 feet.
• A tractor with a 53-foot trailer needs no overlength permit.
• Tractor-doubles have no overall length limit if neither trailer exceeds 28 feet 6 inches and combined trailer length stays within 61 feet.

Those limits are why a Montana dispatcher will ask about your trailer length before your route. If your equipment falls outside them, you need a permit, and some roads will not allow it.

What weight can a Montana truck carry without a permit?

The Trucker's Handbook sets 20,000 pounds on a single axle and 34,000 pounds on a tandem axle without a permit. The maximum gross weight for reducible loads is 131,060 pounds. Vehicles rated 26,000 pounds GVW or more must stop at all open weigh stations, so build the stop into your schedule.

When do Montana trucks need chains or traction devices?

Montana treats winter equipment as a legal requirement, not a suggestion. Chains are required whenever "chains required" signs are posted, and tractor-trailers must carry chains. Motor trucks rated 26,001 pounds GVW or more that tow a trailer must carry approved traction devices from October 1 through April 30. Studded tires are allowed October 1 through May 31. A driver who learns this on the first snowy pass is learning it too late.

What are Montana's truck speed limits and brake rules?

• Trucks over 1 ton rated capacity may travel 70 mph on interstates, day and night.
• Triple trucks and 100-foot doubles are limited to 65 mph on interstates only.
• Compression brakes require a muffler in good working condition.

The two-speed picture is easy to mix up on a long drive, so write the rule for your own equipment on a sticky note until it sticks.

What happens to Montana roads during spring thaw?

As the ground thaws, posted roads may carry lower axle-weight or speed limits. Montana also offers a winter weight permit, which cannot be used on posted bridges or roads. A winter weight permit allows 10 percent excess weight on non-interstate highways, but it does not override what a road or bridge is posted for. On a spring run, read every posting before you commit to a route.

How should you prepare for a Montana mountain route?

Distance and terrain are the real tests. The federal commercial driver material teaches a few habits that matter even more in the mountains:

• Learn to fit your chains before you need them, not on the shoulder in a storm.
• Pick your gear before a long downgrade, and do not rely on the brakes alone.
• Check conditions and postings before you leave, since weather can change over a pass faster than a schedule can.
• Leave extra following distance when roads are wet, icy or posted.

How do you get a Montana CDL?

The Montana MVD page walks through the basics. Hold the commercial learner's permit at least 14 days before the skills test. If you pass the first two skills test steps but fail the on-road portion, you wait at least a week to retest. The vehicle for the skills test must be registered, insured and in good operating condition, and it cannot be a hazmat vehicle. Passed written test results stay valid for one year if you have not yet obtained the CDL. A first-time Class A or B applicant, or anyone adding S, P or H for the first time, completes entry-level driver training.

Taking the skills test in an automatic-transmission vehicle puts the NM restriction on your license, so choose your test truck with your future job in mind.

Rules, permits and seasonal postings change, so confirm current details with the Montana Department of Justice Motor Vehicle Division and Montana Department of Transportation before a run. DMVZone is an independent study resource, not a state agency.