Montana oversize permit rules

What Montana charges for a single-trip OS/OW permit, the limits that trigger one, and the escort thresholds — read from the state’s own publication. This rule has been in effect since 2025-01-01.

Oversize permit

$10

One price for a single-trip permit, whatever the dimensions. A 9-foot-wide load and a 16-foot-wide load pay the same.

Overweight permit

From $10

Scales with distance and weight — there is no single figure.

A load that is both oversize and overweight pays both fees.

+ $20 Permigo service fee per permit, state fees at cost.

Legal limits

Exceed any one of these in Montana and you need a permit for this state.

Limit	Interstate
Width	8'6"
Height	14'0"
Length	80'0"
Gross weight	80,000 lbs
Single axle	20,000 lbs
Tandem axle	34,000 lbs
Trailer length	53'0"

What the permit costs

Montana prices a single-trip permit as flat rate. One price for a single-trip permit, whatever the dimensions. A 9-foot-wide load and a 16-foot-wide load pay the same.

Escort requirements

Thresholds by road class. Where two classes differ, the road you are actually on governs.

Interstate

Width	Requirement
Over 16'6"	1 rear escortINTERSTATE: width over 16'6" to 18' = 1 REAR pilot vehicle (MT Permit Restriction #36a; ARM 18.8.511A(1)(b)(i)). No width escort is required on the Interstate at 16'6" or less — loads 12'7"-16'6" need an escort on non-interstate but NONE on the Interstate.ESCORTS DO NOT STACK ACROSS DIMENSIONS (ARM 18.8.511A(2) verbatim: 'the criteria requiring the greatest number of pilot vehicles will determine the number of pilot vehicles necessary') — a wide AND long load takes the single largest requirement, not the sum; the >17' height-pole front always rides along as equipment. Montana has NO pilot-car certification program; pilots must stay within 1,000 ft (18.8.510A).
Over 18'0"	2 rear escorts · superloadINTERSTATE: width over 18' = at least 2 REAR pilot vehicles side by side (Restriction #36b; ARM 18.8.511A(1)(b)(ii)).Width EXCEEDS 18 ft = Class 1 Superload (MDT Superload Instructions; Restriction #28) — separate superload permit, 2-working-day decision window; TCP + route survey 'may be required on a case-by-case basis' at 18'–20' wide, REQUIRED over 20' (Superload Instructions p.6 document ladder); Class 1 approvals valid 60 days.Loads over 18 ft wide are prohibited on holidays and holiday weekends on the Interstate (Restriction #1c). Otherwise Interstate travel is 24/7 up to 18 ft wide, including weekends (#1a).
Over 20'0"	route survey · superloadWidth over 20': route survey + traffic control plan REQUIRED, plus a breakdown Contingency Plan — the Superload Instructions document ladder tightens INSIDE Class 1 ('Over 20 feet to 34 feet … Traffic Control Plan, Route Survey, … Contingency Plan for breakdowns', p.6).
Over 34'0"	route survey · superloadWidth EXCEEDS 34 ft = Class 2 Superload (Restriction #29): 5-working-day decision window + breakdown contingency plan required.

Height	Requirement
Over 17'0"	1 front escort · height pole · route survey · superloadHeight over 17 ft (to 24 ft) = 1 FRONT pilot vehicle with height pole (Restriction #36c).Height EXCEEDS 17 ft = Class 1 Superload (Superload Instructions; Restriction #28). The route survey must document the setting at which the height pole was calibrated.
Over 24'0"	1 front escort + 1 rear escort · height pole · route survey · superloadHeight over 24 ft = 1 FRONT pilot (height pole) + 1 REAR pilot (Restriction #36d). Height exceeding 24 ft = Class 2 Superload (Restriction #29): 5-working-day window + contingency plan.

Length	Requirement
Over 75'0"	Conditions applyMontana's length-permit onset is 75' COMBINATION length (55' single unit) — but a tractor pulling a ≤53' semitrailer is exempt 'regardless of overall length
Over 150'0"	route survey · superloadLength EXCEEDS 150 ft = Class 1 Superload (Restriction #28). NO length-based pilot-car requirement is published for the INTERSTATE — the length escort triggers (Restrictions #37e/#37f) apply to non-interstate routes. (The 120' rear-pilot clause was the NON-interstate rule from 8/29/2020 until its REPEAL effective 3/21/2026 — MAR Notice 2026-658; it never applied to the Interstate and is dead law now.)
Over 200'0"	route survey · superloadLength EXCEEDS 200 ft = Class 2 Superload (Restriction #29): 5-working-day decision window + breakdown contingency plan.

Weight	Requirement
Over 80,000 lbs	Conditions applyOverweight loads: max speed 55 mph or the posted limit, whichever is less; 10 mph across permit-restricted bridges (ARM 18.8.602(2)). Restricted bridges on the route add pilots — 10-mph crawl bridges: minimum 1 REAR pilot; the eTRIPs-printed DEFAULT for Interstate bridge conditions is NO pilots 'unless additionally added restrictions specify' (#17a/#60); when the interstate centerline condition IS printed, ARM 18.8.602(2)(b)(i) requires minimum 2 REAR pilots — permit-printed condition codes, route-conditional, never auto-billed. All overweight loads must pull into open weigh stations, bypass devices notwithstanding (Restriction #33). Term OW above 10,000 lb excess requires a department Vehicle Weight Analysis (61-10-125(3)(d)).

Weight

Requirement

Over 80,000 lbs

Conditions applyOverweight loads: max speed 55 mph or the posted limit, whichever is less; 10 mph across permit-restricted bridges (ARM 18.8.602(2)). Restricted bridges on the route add pilots — 10-mph crawl bridges: minimum 1 REAR pilot; the eTRIPs-printed DEFAULT for Interstate bridge conditions is NO pilots 'unless additionally added restrictions specify' (#17a/#60); when the interstate centerline condition IS printed, ARM 18.8.602(2)(b)(i) requires minimum 2 REAR pilots — permit-printed condition codes, route-conditional, never auto-billed. All overweight loads must pull into open weigh stations, bypass devices notwithstanding (Restriction #33). Term OW above 10,000 lb excess requires a department Vehicle Weight Analysis (61-10-125(3)(d)).

Non-interstate

Width	Requirement
Over 10'0"	Marking requiredNON-INTERSTATE: the 24/7 travel window only holds up to 10 ft wide (and 150 ft long / 15'6" high) — wider loads travel DAYLIGHT ONLY (Restriction #1b).
Over 12'6"	1 front escortNON-INTERSTATE: width over 12'6" to 16'6" = 1 FRONT pilot vehicle (Restriction #37a; ARM 18.8.511A(1)(a)(i)).Non-interstate holiday rule: loads up to 12'6" wide may travel daylight hours on holidays; wider loads (or >150 ft long / >15'6" high) = NO holiday travel (Restrictions #1d/#1e).ESCORTS DO NOT STACK ACROSS DIMENSIONS (ARM 18.8.511A(2) verbatim: 'the criteria requiring the greatest number of pilot vehicles will determine the number of pilot vehicles necessary') — a wide AND long load takes the single largest requirement, not the sum; the >17' height-pole front always rides along as equipment. Montana has NO pilot-car certification program; pilots must stay within 1,000 ft (18.8.510A).
Over 16'6"	1 front escort + 1 rear escortNON-INTERSTATE: width over 16'6" to 18' = 1 FRONT + 1 REAR pilot vehicle (Restriction #37b; ARM 18.8.511A(1)(a)(ii)).
Over 18'0"	2 front escorts + 1 rear escort · superloadNON-INTERSTATE: width over 18' to 24' = 2 FRONT + 1 REAR pilot vehicles (Restriction #37c; Superload Instructions p.5).Width EXCEEDS 18 ft = Class 1 Superload (Restriction #28) — separate superload permit, 2-working-day decision window; TCP + route survey 'may be required on a case-by-case basis' at 18'–20' wide, REQUIRED over 20' (Superload Instructions p.6 document ladder); Class 1 approvals valid 60 days.Non-interstate loads exceeding 18 ft wide (or 150 ft long / 17 ft high) may NOT travel on weekends (Restriction #1e).
Over 20'0"	route survey · superloadWidth over 20': route survey + traffic control plan REQUIRED, plus a breakdown Contingency Plan — the Superload Instructions document ladder tightens INSIDE Class 1 ('Over 20 feet to 34 feet … Traffic Control Plan, Route Survey, … Contingency Plan for breakdowns', p.6).
Over 24'0"	2 front escorts + 2 rear escortsNON-INTERSTATE: width over 24 ft = 2 FRONT + 2 REAR pilot vehicles (Restriction #37d).
Over 34'0"	route survey · superloadWidth EXCEEDS 34 ft = Class 2 Superload (Restriction #29): 5-working-day decision window + breakdown contingency plan required.

Height	Requirement
Over 15'6"	Marking requiredNON-INTERSTATE: loads over 15'6" high travel DAYLIGHT ONLY (the 24/7 window holds up to 15'6" high — Restriction #1b).
Over 17'0"	1 front escort · height pole · route survey · superloadHeight over 17 ft (to 24 ft) = 1 FRONT pilot vehicle with height pole (Restriction #36c/#36d — applies on Interstate and non-interstate).Height EXCEEDS 17 ft = Class 1 Superload (Restriction #28). The route survey must document the height-pole calibration setting.Non-interstate loads exceeding 17 ft high (or 18 ft wide / 150 ft long) may NOT travel on weekends (Restriction #1e).
Over 24'0"	1 front escort + 1 rear escort · height pole · route survey · superloadHeight over 24 ft = 1 FRONT pilot (height pole) + 1 REAR pilot (Restriction #36d). Height exceeding 24 ft = Class 2 Superload (Restriction #29): 5-working-day window + contingency plan.

Length	Requirement
Over 75'0"	Conditions applyMontana's length-permit onset is 75' COMBINATION length (55' single unit) — but a tractor pulling a ≤53' semitrailer is exempt 'regardless of overall length
Over 150'0"	1 rear escort · route survey · superloadNON-INTERSTATE: length over 150 ft = 1 REAR pilot vehicle (Restriction #37e; ARM 18.8.511A(1)(a)(v)). (ARM 18.8.511A's old 120' rear-pilot clause was REPEALED effective 3/21/2026 — MAR Notice 2026-658; current length escorts start at 150', already superload territory.)Length EXCEEDS 150 ft = Class 1 Superload (Restriction #28) — separate superload permit, route survey + traffic control plan, 2-working-day window.Non-interstate loads exceeding 150 ft long travel daylight only and may NOT travel on weekends (Restrictions #1b/#1e).
Over 200'0"	1 front escort + 1 rear escort · route survey · superloadNON-INTERSTATE: length over 200 ft = 1 FRONT + 1 REAR pilot vehicle (Restriction #37f). Length exceeding 200 ft = Class 2 Superload (Restriction #29): 5-working-day window + contingency plan.

Weight	Requirement
Over 80,000 lbs	Conditions applyOverweight loads: max speed 55 mph or the posted limit, whichever is less; 10 mph across permit-restricted bridges (ARM 18.8.602(2)). Restricted bridges on the route add pilots — 10-mph crawl bridges: minimum 1 REAR pilot; bridge-centerline crossings on NON-interstate routes: 1 FRONT + 1 REAR pilot (18.8.602(2)(b)(ii)) — route-conditional, not auto-billed. All overweight loads must pull into open weigh stations, bypass devices notwithstanding (Restriction #33). Term OW above 10,000 lb excess requires a department Vehicle Weight Analysis (61-10-125(3)(d)).

Weight

Requirement

Over 80,000 lbs

Conditions applyOverweight loads: max speed 55 mph or the posted limit, whichever is less; 10 mph across permit-restricted bridges (ARM 18.8.602(2)). Restricted bridges on the route add pilots — 10-mph crawl bridges: minimum 1 REAR pilot; bridge-centerline crossings on NON-interstate routes: 1 FRONT + 1 REAR pilot (18.8.602(2)(b)(ii)) — route-conditional, not auto-billed. All overweight loads must pull into open weigh stations, bypass devices notwithstanding (Restriction #33). Term OW above 10,000 lb excess requires a department Vehicle Weight Analysis (61-10-125(3)(d)).

Movement restrictions

Restriction	In Montana
Night travel	Daylight hours only
Weekends	No blanket restriction
Holidays	No blanket restriction

Movement hours

Situation	Window
Interstate ≤18′ wide	24/7 — weekends, holidays, holiday weekends included (#1a/#1c)
Interstate >18′ wide	no holiday or holiday-weekend travel (#1c)
Non-interstate ≤10′W · ≤150′L · ≤15′6″H	24/7, holidays included (#1b/#1d)
Non-interstate >10′W (to 12′6″) or >150′L or >15′6″H	daylight only — ½ hr before sunrise → ½ hr after sunset (ARM 18.8.101(3)); >10′–12′6″W keeps daylight holiday travel (#1d)
Non-interstate >12′6″W (or >150′L / >15′6″H)	no holiday / holiday-weekend travel (#1d)
Non-interstate >18′W / >150′L / >17′H	no weekend travel (#1e)
Holidays (6)	New Year's · Memorial · July 4 · Labor · Thanksgiving (blocks Thu–Sun) · Christmas; Fri/Sat holiday blocks Fri–Sun, Sun/Mon blocks Sat–Mon, midweek blocks that day (ARM 18.8.101(6)-(7))
Overweight loads	max 55 mph or posted, whichever less; 10 mph on restricted bridges (ARM 18.8.602(2)); must enter open weigh stations (#33)
Superloads	same windows; MDT may limit days/hours per permit; MCS administrator may waive any travel restriction (ARM 18.8.509(10)-(11))
Severe conditions	no travel when the route is under severe driving conditions (#39)

Where these permits come from

If you file yourself, this is the office you are dealing with. Check the linked page — some states issue OS/OW permits through their highway patrol or revenue department rather than the DOT.

	Montana permit office

MCA 2025 (61-10-102/-103/-104/-107/-124/-125; 124 amd. Ch.45+Ch.47 L.2025 · mca.legmt.gov · in effect since 2025-01-01. Fees and rules change; the linked document is always the authority.