Montana Oversize Permit Requirements and Legal Dimensions

In Montana, you need an oversize permit whenever a vehicle or load exceeds the state's legal dimensions: 8 feet 6 inches in width, 14 feet in height, or specific length limits based on the configuration, such as 75 feet for a tractor-semitrailer combination. The Montana Department of Transportation (MDT) mandates these permits to ensure safety on mountain passes, narrow bridge spans, and heavy traffic corridors like I-90 and U.S. 93. Failure to secure a permit before entering the state or moving the load can result in fines, mandatory offloading, and vehicle impoundment. DispatchTool helps carriers manage these compliance hurdles by integrating Montana’s specific bridge and clearance data directly into truck-safe routing. Dispatchers can use the platform to plan routes that avoid the 13-foot 6-inch clearances found on certain secondary routes and store permit documentation for instant driver access. Before moving a non-divisible load through Big Sky Country, create a DispatchTool account to verify your route against national bridge law and state-specific width restrictions.

Legal Dimensions and Weight Limits

Montana law defines legal vehicle dimensions under MCA 61-10-101 through 61-10-104. A vehicle is considered legal if it does not exceed a total width of 102 inches (8'6") and a total height of 14 feet. Length limits vary by configuration: a single unit is limited to 55 feet, while a tractor-semitrailer combination is generally limited to 75 feet, provided the trailer does not exceed 53 feet. Weight is also a factor; the gross vehicle weight must not exceed 80,000 pounds on the interstate system without a permit, following the Federal Bridge Formula. If any of these thresholds are crossed, an Oversize/Overweight (OSOW) permit is required from the MDT Motor Carrier Services (MCS) division.

Permit Types and Costs

Montana offers several permit options depending on the frequency of travel. Single-trip permits are valid for 72 hours and are typically priced based on the nature of the load and the excess weight, starting at a base fee of $10.00 for oversize only. For carriers moving loads frequently, Term Permits (Annuals) are available. An annual permit for oversize width (up to 15 feet) or length typically costs $75.00. Overweight permits are calculated using a mileage-based fee structure or a flat annual fee if the weight is within specific ranges, such as the 10% tolerance for certain agricultural products. All applications are processed through the MCS ePart system.

Escort Vehicle Requirements

Escort vehicles, or pilot cars, are mandatory in Montana when a load's dimensions pose a risk to other traffic. For travel on two-lane highways, one escort is required if the width exceeds 12 feet, and two escorts (front and rear) are required if the width exceeds 14 feet. On interstate highways, a rear escort is generally required for widths exceeding 15 feet. If a load exceeds 16 feet 6 inches in height, the carrier must coordinate with utility companies to ensure clearance of overhead lines. Escort drivers must be at least 18 years old and operate a vehicle equipped with a sign reading 'Oversize Load' that is at least 5 feet long and 12 inches high.

Restricted Travel Times and Holidays

Montana enforces strict travel time restrictions for oversize loads to mitigate congestion. Movement is generally restricted to daylight hours, defined as one-half hour before sunrise to one-half hour after sunset. Loads exceeding 10 feet in width are not permitted to travel after 4:00 PM on Fridays until sunrise on Saturday during the summer months (Memorial Day through Labor Day) on high-traffic routes. Furthermore, travel is prohibited on major holidays including New Year's Day, Memorial Day, Independence Day, Labor Day, Thanksgiving, and Christmas. If weather conditions include wind speeds over 25 mph or visibility less than 500 feet, all oversize operations must cease.

Signage and Lighting Standards

Every oversize vehicle in Montana must be marked with signs and flags to alert the public. 'Oversize Load' signs must be mounted on the front and rear of the vehicle, featuring black letters at least 8 inches high on a yellow background. Red or orange fluorescent flags, minimum 18 inches square, must be placed at the four corners of the extremities of any wide load. When traveling under a permit that allows night movement, the extremities must be illuminated with amber lights to the front and side, and red lights to the rear, visible from a distance of at least 500 feet.

Bridge and Route Restrictions

Montana is known for its mountainous terrain and aging bridge infrastructure on secondary roads. The MDT maintains a Restricted Routes Map which details vertical clearances as low as 13 feet 0 inches and bridge weight ratings that may be significantly lower than the 80,000-pound interstate standard. Carriers must verify their specific axle weights against the Montana Bridge Table 1 and Table 2. Any load exceeding 18 feet in width or 17 feet in height is classified as a 'Superload,' requiring a specialized engineering review by MDT which can take up to 30 days to process and involves significantly higher administrative fees.

Sources

Montana Department of Transportation (MDT) Motor Carrier Services (2024) — https://www.mdt.mt.gov/mcs/ Montana Code Annotated (MCA) Title 61 Chapter 10 (2023) — https://leg.mt.gov/bills/mca/title_0610/chapter_0100/parts_index.html Federal Highway Administration (FHWA) Bridge Formula Weights (2024) — https://ops.fhwa.dot.gov/freight/publications/brdg_frm_wghts/

Frequently asked

What is the maximum width allowed without a permit in Montana?

The maximum legal width in Montana is 8 feet 6 inches (102 inches). Any load wider than this requires a single-trip or annual oversize permit from the MDT.

How much does a Montana oversize permit cost?

A basic single-trip oversize permit starts at $10.00, while annual permits for width or length are typically $75.00. Overweight fees are calculated based on a per-mile rate or specific weight brackets.

Are oversize loads allowed to travel at night in Montana?

Generally, no. Oversize travel is restricted to daylight hours. However, loads that are only overweight (not oversize) or loads that do not exceed 10 feet wide on specific routes may receive authorization for night travel if properly lighted.

When does a load require a pilot car in Montana?

On two-lane roads, a pilot car is required for widths over 12 feet. On interstates, a pilot car is required for widths exceeding 15 feet. Loads over 105 feet long also require an escort.

Does Montana allow 'Double-Wide' manufactured homes?

Yes, but they require specific permits. Manufactured homes up to 16 feet wide can be moved with a standard permit and escorts, but anything over 16 feet wide is considered a Superload.