Montana Oversize / Overweight Permit Requirements
Legal-without-permit dimension limits, escort and pilot car thresholds, height pole rules, daylight-only windows, and holiday restrictions for Montana oversize moves.
Legal limits without a permit
In Montana, you can move a load without an OSOW permit up to these dimensions on the Interstate and designated highways. Anything over the limits requires a permit (and may require escorts — see below).
| Dimension | Without a permit | Permit required when |
|---|---|---|
| Width | 8′6″ (federal limit) | Anything wider |
| Height | 13′6″ | Anything taller |
| Combo length | 75′0″ | Anything longer |
| Gross weight | 80,000 lb | Anything heavier |
Escort and pilot car thresholds
When permitted, the following escort or movement-restriction rules apply in Montana. Thresholds are conservative — your specific permit conditions may impose tighter limits depending on the route.
| Trigger | Dimension | Threshold | Detail |
|---|---|---|---|
| Rear pilot car | Length | 105'0" | Rear pilot added at lengths over 105' on all highways; lead+chase both required (ARM 18.8.1605). |
| Front pilot car | Length | 85'0" | Front pilot required on 2-lane roads for overall lengths over 85' (ARM 18.8.1605). |
| Police escort | Width | 20'0" | Montana Highway Patrol escort required for widths over 20' or as specified in permit conditions (ARM 18.8.1602). |
| Rear pilot car | Width | 16'0" | Rear pilot car added when width exceeds 16'. Lead+chase both required on all route types (ARM 18.8.1602). |
| Height pole | Height | 15'0" | Front pilot car must carry height-clearance pole for loads over 15' tall (ARM 18.8.1601). |
| Front pilot car | Width | 14'0" | Front pilot car required on 2-lane highways for widths over 14'. On divided/Interstate, pilot required at same threshold (ARM 18.8.1602). |
| Certified escort required | Width | 14'0" | Montana escort vehicle operators must be certified through MDT's escort certification program (ARM 18.8.1601). |
| Daylight-only movement | Width | 14'0" | Loads over 14' wide restricted to daylight hours (1/2 hr after sunrise to 1/2 hr before sunset). Night movement requires special permit endorsement (ARM 18.8.1601). |
| Weekend / holiday restriction | Width | 14'0" | No movement on New Year's, Memorial Day, Independence Day, Labor Day, Thanksgiving, Christmas. Restrictions begin noon preceding day for loads over 14' wide (ARM 18.8.1601). |
Stop tracking these rules by hand.
OverSizeTMS encodes the per-state escort and dimension rules for every state plus DC. Enter the load dimensions and route, and the platform tells you which permits, escorts, and time windows apply automatically.
See how it works →Last updated 2026-06-06. Cross-checked against the state admin code.