Montana Oversize Load Permits, Regulations & Axle Rules

Montana's travel rules hinge on two variables, road class and how far a load exceeds legal dimensions, and the permitted window shrinks fast once you tip past certain thresholds on non-interstate routes.

On the Interstate, loads up to 18 feet wide move around the clock, seven days a week, with no daylight requirement. That 24/7 window holds even on weekends, and it holds on most holidays. The only Interstate shutdown is for loads wider than 18 feet, which are prohibited from moving on any holiday or holiday weekend at all. There is no rush-hour curfew in Montana and no metro-area blackout period anywhere in the state.

Non-interstate highways operate differently. Loads within 10 feet wide, 150 feet long, and 15'6" high may also run 24/7. Once any one of those numbers is exceeded, the load is restricted to daylight hours only. Push past 12'6" wide, 150 feet long, or 15'6" high on non-interstate roads and the load loses holiday and holiday weekend travel entirely. An additional layer kicks in for the widest and longest non-interstate moves: loads over 18 feet wide, over 150 feet long, or over 17 feet high are banned from weekend travel as well, so Saturday and Sunday are off the table.

Montana recognizes six holidays: New Year's Day, Memorial Day, Independence Day, Labor Day, Thanksgiving, and Christmas. The blocked period is not just the calendar day, it expands based on the day of the week the holiday falls. A holiday on Friday or Saturday kills Friday through Sunday. A holiday on Sunday or Monday kills Saturday through Monday. Thanksgiving always claims Thursday through Sunday.

Travel stops for any route placed under severe driving conditions as determined by the Montana Department of Transportation. No specific visibility distance or wind threshold is published; the department makes the call. Separately, when a load requires pilot vehicles, the permittee may not delay normal traffic more than 15 minutes. Montana does not allow 24-hour continuous movement for any load type; the daylight and weather rules stand without exception.

Montana's commodity rules reflect the realities of Big Sky Country: logging, hay, and heavy-equipment moves that would be oddities elsewhere are routine here.

Raw logs on a truck or tractor with a single pole trailer or semi-trailer may be up to 9 feet wide, 75 feet long, and 15'6" high without a width permit; other log combinations are capped at 95 feet overall. Rear overhang on log loads is limited to 15 feet, measured from the center of the last axle to the end of the rearmost log. A term permit's length relief does not extend to log combinations: loads over 75 feet need a single-trip permit. Utility poles, however, are carved out entirely, exempt from both the 75-foot log length limit and the 15-foot overhang limit.

Baled hay gets tiered width allowances: small square bales are allowed up to 9'6" wide, large square bales without a hay rack up to 10 feet, and large round bales or loads using hay racks up to 12 feet. All hay loads are capped at 15'6" high. Double hay trailer combinations may run up to 88 feet of combined trailer length.

Logging equipment, distinct from raw log loads, may be up to 15 feet wide, 15'6" high, and 95 feet long on permit.

Snow removal equipment is essentially exempt from the general oversize travel framework while working. Equipment up to 18 feet wide on a single-trip permit (or 15 feet on a term permit) may run 24 hours a day, seven days a week on any highway during active snow removal operations, including nights, weekends, and holidays. Pilot vehicle requirements and oversize sign requirements both disappear for this category while engaged in removal.

Implement dealers have their own permit category that is not subject to weekend or holiday travel restrictions, though lighting and pilot vehicle requirements still apply based on actual dimensions.

Implements of husbandry and hay vehicles operated within 100 miles of a farming operation may exceed the standard 8'6" width limit during daylight hours without a permit for the excess width. Loads over 12'6" wide in this category must be preceded by a flag vehicle unless the equipment is hauling or towing implements of husbandry, construction equipment, or forestry equipment at highway speed; in that case, the rear pilot vehicle requirement is waived by statute.

Stinger-steered auto and boat transporters run under a specialized length rule: up to 80 feet of combination length plus 4 feet of front overhang and 6 feet of rear overhang.

Montana uses the term Superload and structures it into three classes with distinct triggers, review timelines, and documentation requirements. Any load that exceeds 18 feet in width, 17 feet in height, 150 feet in length, or that requires the MDT Bridge Bureau's approval because of weight, truck configuration, or route characteristics qualifies as a Superload.

Class 1 covers loads from just over 18 feet wide up to 34 feet, from just over 17 feet high up to 24 feet, and from just over 150 feet long up to 200 feet. The appropriate district administrator must approve a completed application, and the department must issue a decision within two working days of receiving a properly completed submittal. The permit is valid for 60 days from approval.

Class 2 covers loads exceeding 34 feet wide, 24 feet high, or 200 feet long. The same district administrator review applies, but the deadline extends to five working days. The permit is also valid for 60 days, and the department may impose additional conditions including local government or utility approval, a specific insurance requirement, a travel plan, or a traffic control plan.

Class 3 is the weight-only tier. The load's dimensions must stay within Class 1 limits (no wider than 18 feet, no taller than 17 feet, no longer than 150 feet), but the weight or truck configuration requires Bridge Bureau review. Class 3 permits are valid for one year, the longest duration in the system, and can cover the reverse route if no interstate is involved.

Required documents scale with dimensions. All Superload applications call for a contact list (cities, counties, and tribal governments on non-interstate routes), a configuration diagram with axle spacings and weights, and insurance certification. A traffic control plan and route survey become mandatory for loads over 20 feet wide. Loads over 20 feet wide add a phone number for a load supervisor and a contingency plan for breakdowns. Height Superloads over 17 feet add a utility worksheet and telephone letters to affected utility companies. Any route crossing a railroad requires advance notification to each railroad before movement. There is no published fee structure specific to Superload applications; standard permit fees apply. Insurance must meet a minimum of $1,000,000 combined single limit per occurrence.

Montana requires a formal route survey for every Superload, and it is the carrier's responsibility; the state does not conduct it. The survey must document six elements: the date the route was run; mile posts where the load can safely pull over to allow traffic to pass; a written explanation of how traffic will not be delayed beyond 15 minutes at any point; if the Superload is for height, the setting at which the height pole was calibrated; a complete list of conflicts along the route (wire span lights, overhead signs, traffic signals, delineators, and similar obstructions); and written permission letters for any private property that will be used for parking or crossing.

Height Superloads over 17 feet also require a utility worksheet listing all affected overhead utilities and telephone letters sent to each. The route survey and traffic control plan are part of the application package: they are prerequisites to permit approval, not documents filed after the fact.

Beyond formal Superloads, Montana places route-clearance responsibility squarely on the permittee for all permitted moves. Structure height signs along state routes are advisory only; MDT explicitly does not warrant or guarantee their accuracy. The carrier is responsible for physically verifying clearance on any route before the move, regardless of what posted signs say.

Route-specific restrictions exist on two corridors that reduce effective maximum widths well below the general permit ceiling: MT-35 between Polson and Bigfork is restricted to 9 feet wide, and US-87 between Belt and Raynesford is restricted to 12'6" wide. Any route planning through these corridors must account for these permanent restrictions.

Montana has no codified dimensional or weight threshold that mandates a law-enforcement escort. The Montana Highway Patrol (MHP) is the state agency involved in oversize movement enforcement, and Motor Carrier Services (MCS) Enforcement Bureau officers are also Montana Peace Officers authorized to enforce commercial vehicle laws, but neither agency is triggered automatically by a load's size or weight.

Traffic control for oversize and Superload moves in Montana is handled by civilian pilot vehicles (the state's own term for escort vehicles), not police escorts. A Superload does, however, carry a pre-move notification requirement to all local emergency services (law enforcement, fire, and ambulance) within every jurisdiction along the route. That notification must include the route, time, and date of the move so emergency services can make contingency arrangements. This is a coordination obligation, not an escort mandate.

At the discretion of the MCS administrator or designee, any restricted travel condition may be waived for a Superload. On the heaviest moves, MDT's Bridge Bureau may also place speed restrictions on Interstate routes that require additional pilot cars, signage, and a formal Traffic Control Plan, but these remain pilot vehicle requirements, not sworn-officer escorts.

For loads that do require pilot vehicles, Montana's rules are specific: each pilot vehicle must remain within 1,000 feet of the permitted load at all times, must carry oversize load signs and flashing amber lights matching the requirements of the transport vehicle, and must maintain two-way communication capability. Pilot vehicles must be at least 60 inches wide and may not exceed 14,000 lbs GVWR (26,001 lbs for service or mechanic trucks contracted by the permittee).