Idaho Oversize Load Permits, Regulations & Axle Rules

Idaho organizes oversize travel around a three-tier route color system, RED, BLACK, and INTERSTATE, and the tier determines almost everything about when a permitted load can move. Knowing which color your route falls on is the first step in planning any move here.

Red-coded routes are the most restrictive. Travel is daylight only, no Saturday or Sunday movement, and the no-travel window starts at 2:00 p.m. on Friday (or the afternoon before any designated holiday). Travel may not resume until sunrise on Monday or the morning after the holiday. Single-trip permits carry a limited exception for very early weekend movement, from dawn to 8:00 a.m. on Saturday or Sunday, but the load must reach a safe parking spot by 8:00 a.m. or stop where it is.

Black-coded and Interstate routes are more flexible. Any load at or under 12 feet wide, 120 feet long, and 15 feet high may run 24 hours a day, seven days a week on those roads, including holidays. Once a load exceeds any one of those three thresholds, it falls under the ITD Pilot/Escort Vehicle Travel Map restrictions. On black-coded routes, loads in the upper tier must stop moving before 4:00 p.m. on the day before a designated holiday and may not resume until sunrise the following morning.

Idaho recognizes six holidays: New Year's Day, Memorial Day, Independence Day, Labor Day, Thanksgiving, and Christmas.

Any load over 13 feet wide faces a metro commuter curfew on all route types. Movement is prohibited from 6:00 a.m. to 9:00 a.m. and from 4:00 p.m. to 6:30 p.m., Monday through Friday, in and around Boise valley (I-84, mileposts 26 to 59), Coeur d'Alene (I-90, mileposts 0 to 17), Idaho Falls (I-15, mileposts 115 to 121), Twin Falls (US-93, mileposts 41 to 53), and several smaller communities including Eagle, Emmett, Garden City, Middleton, Pocatello valley, and Star.

A load with more than 7 feet of front overhang is restricted to daylight travel on two-lane, two-way highways regardless of route color.

Weather invalidates any permit automatically. Loads must stop and wait out ice, snow, frost, excessive water, mud, winds over 40 mph, visibility below 500 feet, roadway obstructions, or a declared emergency. There is no continuous 24-hour movement exception for any load type. Even the most flexible black-coded and Interstate permits are subject to weather invalidation and the commuter curfew.

Idaho carves out several commodity types with their own dimensional allowances, equipment standards, or travel conditions.

Implements of husbandry and farm tractors get meaningful exemptions from width rules. On non-interstate roads, an implement of husbandry may move farm-to-farm or to and from a dealer, repair shop, or auction during daylight without a permit, provided the farmer or a designated agent is operating it. Farm tractors transported on the Interstate require a special permit once width exceeds 9 feet; on non-Interstate roads, the threshold drops to 8'6". An overwidth trailer used to transport an implement farm-to-farm shares the same exemption as long as it isn't wider than the implement itself.

Cylindrical hay bales may be hauled two bales wide and two bales high on an annual permit, up to 11'6" wide. The hauling combination may not exceed 68 feet of trailers (including connecting tongue) or 80 feet overall.

Kiln lumber stacks may be transported two stacks wide and two stacks high on designated highways, up to 9'3" wide.

Poles, pipes, logs, and structural members carried on a stinger-steered pole trailer or log dolly connected by a reach or pole may run up to 75 feet overall as a statutory configuration. On the first movement out of the forest, tree-length logs or poles up to 110 feet overall are exempt from the escort requirement. Secondary movements must comply with the Pilot/Escort Vehicle Travel Map.

Divisible loads between 14 and 15 feet high may be permitted on designated highways as long as the vehicle itself does not exceed 14 feet.

Disabled vehicles are covered by an annual wrecker permit. Time-of-travel restrictions are waived for the first movement needed to clear the travel way. Height is capped at 15 feet, and a front pilot/escort vehicle is required when moving a vehicle wider than 10 feet at night.

Idaho does not use the term "superload" anywhere in its permit regulations. The functional equivalent is a load that triggers district approval, which requires up to 24 working hours of additional lead time on top of standard permitting. Any one of the following dimensions puts a load into that review:

- Width greater than 16 feet on RED or BLACK routes - Width greater than 18 feet on Interstate - Height greater than 16 feet on any route - Overall length greater than 120 feet on non-Interstate routes - Overall length greater than 150 feet on Interstate

The 24-working-hour clock runs after the completed application is submitted, so a move requiring district approval cannot be issued same-day. The Department's standard is a "reasonable determination of the necessity and feasibility of the proposed movement," and applicants must supply all information the Department requests to support that engineering determination.

Loads in the district-approval tier that will travel on two-lane highways face an additional requirement: a traffic control plan prepared by a licensed engineer or an ATSSA-certified traffic control supervisor. That plan is mandatory when width exceeds 18 feet, overall length exceeds 150 feet, or height exceeds 16 feet on a two-lane road. It must identify pull-over locations by milepost for traffic relief, lay out the pilot car and traffic control personnel assignments, list railroad crossings with emergency contacts, and address how emergency vehicles will navigate around the load.

On the weight side, the equivalent review is a bridge analysis. Any single axle or steer axle over 35,000 pounds triggers bridge approval before the permit issues. For loads at or under 250,000 pounds gross, the Department takes up to 3 business days for the analysis. Loads over 250,000 pounds allow up to 10 business days. Once gross weight exceeds 800,000 pounds, the carrier must commission an independent third-party bridge analysis, which the Department then reviews and acts on. Multiple route configurations or multiple route options for the same move also require third-party analysis. The Department may waive engineering analysis if it already holds sufficient prior analyses for similar load configurations on the same route.

One special corridor applies additional review obligations entirely independent of the district-approval framework. The United States Forest Service administers oversize loads on US-12 from milepost 74 to milepost 174 through the Nez Perce-Clearwater National Forest. Loads meeting any of the following Forest Service criteria must undergo a separate review: more than 16 feet wide, more than 150,000 pounds, more than 150 feet long, or requiring more than 12 hours to transit the corridor. Only one such load may be on this section of US-12 at any one time.

Idaho's route review is built around two separate obligations that can both apply to the same move: a departmental feasibility determination and, in the right conditions, a carrier-performed utility clearance.

The feasibility determination is essentially Idaho's equivalent of a formal route survey. The Idaho Transportation Department (ITD) conditions permit issuance on its engineering determination that the movement is necessary and feasible. For loads at or under the district-approval thresholds, this is handled during normal permit processing. Once a load crosses any district-approval trigger (more than 16 feet wide on RED or BLACK routes, more than 18 feet wide on Interstate, more than 16 feet high, more than 120 feet long off Interstate, or more than 150 feet long on Interstate), the Department may take up to 24 working hours for that evaluation, and it must be completed before the permit is issued.

For over-height loads, the route evaluation focuses on vertical clearances. Any over-height permit is conditioned on the Department's review of every structure along the proposed route. At 16'6" in height, the carrier must give advance notice if there are overhead traffic signals on the route. Above 16'6", the carrier must contact local utility companies directly to obtain approval and assistance with power lines before the move proceeds. This utility notification is a carrier-side obligation, not something the Department handles on the applicant's behalf.

Bridge weight analysis functions as the structural component of route review. The Department evaluates every structure on the route for loads requiring bridge analysis, and that analysis must be complete before a permit is issued; the permit is withheld until the engineering work is done. For loads over 800,000 pounds, the third-party analysis document itself must be submitted to the Department as part of the application. On the Nez Perce-Clearwater Forest corridor (US-12, MP 74 to 174), an Idaho State Police vehicle safety inspection is required before any qualifying load's permit can be issued, and the load may be required to travel at night through that section.

There is no Idaho rule requiring a carrier to perform a general physical pre-trip survey on standard oversize loads. The state's route analysis is performed by the Department for loads triggering district approval, and carrier obligations are specific: utility notification above 16'6" and bridge analysis commissioning above 800,000 pounds.

Idaho does not publish a dimensional threshold that requires a law-enforcement escort on general state highways. The Idaho State Police (ISP) is the relevant agency, but police escort involvement is discretionary across the standard permit population, attached to specific moves case by case rather than automatically triggered by width, height, length, or weight numbers.

The one context where ISP involvement is more structured is the Nez Perce-Clearwater Forest corridor on US-12 between mileposts 74 and 174. Loads meeting the Forest Service criteria for that section (over 16 feet wide, over 150,000 pounds, over 150 feet long, or requiring more than 12 hours to transit) may be required to have ambulances and law enforcement escorts as a condition of movement. That determination is made through the Forest Service review process rather than by the ITD permit office alone. In addition, every load subject to those Forest Service criteria must pass an ISP vehicle safety inspection before the permit is issued.

For all other routes and loads, civilian pilot/escort vehicles handle the codified escort requirements. Those requirements are set by the ITD Pilot/Escort Vehicle Travel and Vertical Clearance of Structures Map, and they vary significantly by route tier. On RED routes, any load over 8'6" wide requires at least one front escort, and anything over 10' wide needs front and rear escorts. On BLACK routes, escorted width starts at 12 feet for a single front escort and 14 feet for front-and-rear. On Interstate, a single rear escort applies from 15'1" to 18' wide. Loads over 16 feet high require a front escort carrying a non-metallic, non-conductive height pole with a flexible tip, on every route type. Civilian pilot/escort vehicles must be passenger cars or trucks weighing no more than 16,000 pounds GVW and may not tow trailers. In rural areas, escorts maintain approximately 1,000 feet of spacing from the permitted load; that gap may be reduced in urban areas for turning movements.

Because no dimensional threshold forces ISP coordination, carriers should not assume a police escort will be automatically arranged as part of the permit process. If ITD determines law-enforcement presence is warranted on a particular move, that will be communicated through the permitting process.