Montana OS/OD Overview
Permit Required
Yes – all oversize or overweight loads require a permit from the Montana Department of Transportation (MDT).
Legal Limits (Without Permit)
- Width: 8'6"
- Height: 14'
- Length: 75' (combo); 53' trailer
- Weight: 80,000 lbs GVW (with standard axle limits)
Permitted Load Maximums (Typical Upper Limits)
- Width: Up to 18' with proper escorting
- Height: Over 16' requires route survey and utility coordination
- Length: Over 120' allowed with review
- Weight: Over 250,000 lbs with engineering analysis and bridge clearance
Superloads require advance coordination with MDT’s Engineering and Permitting offices.
Travel Hours
- Standard: ½ hour before sunrise to ½ hour after sunset
- Weekend: Travel allowed with restrictions for wider/heavier loads
- Holidays: No travel on major holidays or after noon the day before
- Night travel: Allowed for loads under 10' wide and 110' long with proper lighting
Escort Requirements (General Guidelines)
| Dimension | Escort Requirement |
|---|---|
| Width > 12' | 1 Escort (rear or front depending on road type) |
| Width > 14' | 2 Escorts (front and rear) |
| Height > 16' | High pole escort and approved route survey |
| Length > 120' | 1 or 2 Escorts based on configuration and route |
Additional Notes
- Oversize Load signs, red/orange flags, and amber lights are required
- Mountain passes, frost laws, and bridge limits must be checked carefully in Montana
- Permits issued through the Montana Motor Carrier Services online system
Detailed Information
PERMITS: valid for three to five days
OPERATING TIME: Loads not exceeding 10' wide, 14'6" high, or 110' in length may travel 24/7 on all routes. Daylight hours (½ hour before sunrise to ½ hour after sunset), including Saturdays and Sundays, is allowed for loads not exceeding 18' wide, 18' high, or 120' in length except on Red Route highways. DW21 and 5 MPH conditions on 2-lane highways only allow daytime travel.
RESTRICTED TRAVEL: On Red Route Highways, travel is not allowed after 3:00 P.M. Fridays until Sunrise on Saturday, and from 12:00 Noon Sunday to sunrise on Monday if dimensions exceed 10' wide, 14'6" high or 110' in length; and no travel is allowed after 4:00 P.M. Friday until Monday morning if dimensions exceed 18' wide, 18' high, or 120' in length. Red Route Map is available online or at scales. Holiday travel is usually allowed for loads not exceeding 10' wide, 14'6" high or 110' long.
LEGAL DIMENSIONS: Width: 8'6” Height: 14' Length: 53' semi-trailer, 75' maximum length if trailer exceeds 53' or if there is any rear overhang Overhang: Overall length including overhang up to and including 75' is legal. Over 75' needs permit. Weight: 80,000 Gross Single – 20,000 Tandem – 34,000 Tridem – 42,000 Divisible Loads Exceeding 80,000: You can exceed 80,000 gross without a permit as long as you are legal on all axle/group weights and you are licensed for at least the amount of your gross weight.
ROUTINE PERMIT LIMITS: Width: 18' Height: 17' Length: 150' Weight: * (5 axles) * (6 axles) * (7 axles) *Depends on spacings Single – 24,000 Tandem – 48,000* Tridem – 62,700* * Variable, dependent on axle spacings You must be registered for at least the amount of weight you are permitting for Montana. * Note: DW21 Conditions: Over approximately 54,300 pounds (depending on axle spacings) on a Tridem on 2-lane highways triggers DW21 Conditions, requiring 2 pilot cars. Over approximately 48,000 (depending on axle spacings) on a Tridem on 2-lane roads may trigger 5MPH Conditions which does not require pilot cars but restricts running to daylight only. Loads in excess of these dimensions are considered as superloads.
ESCORTS: On Interstate Highways: Width: Over 16'6" – 1 escort have 2-lane detours. Height: Length: Over 120' – 1 escort Not usually required, but over 17' may depend on route, and over 16' may On 2-Lane Highways: Width: Over 12'6" – 1 escort, over 14’ – 2 escorts Height: Over 17' – 1 escort with high pole Length: Over 110' – 1 escort Weight: Over 54,300 – 55,000 on a Tridem (varies with spacings) – 2 escorts (DW21 Conditions).
SIGNS, FLAGS & LIGHTS: Vehicle/load exceeding 10' in width require "Oversize Load" signs front and rear, and 5" flashing amber lights, revolving beacon or strobe light(s) are required at each end of the Oversize Load sign on the power unit, or a single beacon light may be used on top of the power unit as long as it is visible from all directions. If the light is blocked by the height/width of the load, the rear of the load should also have a light. "Long Load" sign must be displayed on the rear of combinations exceeding 105' on non-Interstate routes, and exceeding 120' on Interstate routes. Overlength load does not need signs if less than 110' total overall length.
SEASONAL LOAD (WEIGHT) RESTRICTIONS: Spring thaw restrictions may occur on some routes approximately February through May. Interstate routes are usually not affected. Check with Permits Office.