The rules are state rules
The single most important thing to understand about oversize freight: there is no national oversize permit. The federal government sets a floor; each state owns everything above it.
What Washington sets
- 102 inches (8'6") wide on the National Network of highways, from the Surface Transportation Assistance Act of 1982. States cannot go stricter on those roads.
- 80,000 lbs gross, 20,000 lbs on a single axle, 34,000 lbs on a tandem, on the Interstate.
- Bridge Formula B, which caps weight based on how far apart your axles are: W = 500(LN⁄(N−1) + 12N + 36). More axles, more spread, more legal weight.
- No federal height limit at all. Height is purely a state matter.
What the states own
- Height limits: 13'6" or 14' depending on the state.
- Every oversize and overweight permit: fees, forms, processing times.
- Escort triggers: at what width, height, or length a pilot car is required.
- Travel restrictions: daylight rules, weekend bans, holiday blackouts.
- Superload thresholds and the engineering review behind them.
Legal limits, and where they bend
Cross any one of these four lines and the load is over-dimensional. The width and weight lines barely move state to state. Height and length move a lot, and knowing where saves real money.
Legal height by state
| Limit | States |
|---|---|
| 13'6" | The East, Midwest, and South: 32 states including GA, PA, IL, OH, FL, NY, plus HI and DC |
| 14'0" | TX, CA, AZ, NV, OR, WA, ID, MT, UT, NM, NC, ND, SD, WY, KS, MO |
| 14'6" | CO, NE |
| 15'0" | AK statewide; the Dalton Highway haul road to Prudhoe Bay runs to 17' |
Legal length (overall) by state
| Limit | States |
|---|---|
| 55' | MD, the strictest in the country |
| 60' | AR, DE, IN, NC |
| 65' | AZ, CA, HI, IL, KY, NY, OH, TX |
| 70'–75' | Most of the country: 35 states |
| 99'–100' | MS, GA, the lenient end |
Trailer math
Road height is deck height plus cargo height. The trailer choice decides whether a tall load needs a permit chain or moves as ordinary legal freight.
Standard flatbed
Legal cargo up to 8'6" tall in 13'6" states. Pipe, steel, lumber, machinery that loads by crane.
Step deck
Legal cargo up to 10'0" tall. Tall machinery without the lowboy day rate.
RGN / lowboy
Legal cargo up to 11'6"–12' tall. The gooseneck detaches so tracked equipment drives on.
Slide the load Interactive
Drag the sliders and watch what turns a legal load into a permit chain.
Permits: what they cost, how they work
The permit itself is usually the cheapest line on the quote. What matters is the process around it: who files, what the permit actually says, and the clock that starts when it issues.
Oversize (OS)
- Any dimension over the state's legal limit
- Base single-trip fee: $5–$75 per state. Florida $5, Oregon $8, Texas $60, Ohio $75
- Routine issue: same day to 2 business days in most states
- The load must be non-divisible: if it can reasonably be broken down to legal size, states expect you to break it down
Overweight (OW)
- Gross over 80,000 lbs, or any axle group over its limit
- Weight-and-distance fees stack on the base: several hundred dollars per state is normal for real weight
- Texas example: $60 base plus $210–$470 by weight bracket
- Axle configuration is part of the application. The state is checking bridges, not just the total
What a first-timer doesn't know about the permit itself
- The carrier pulls the permit in nearly every case. Permits are issued to the specific vehicle and carrier running the load, so the carrier applies. A broker will occasionally file on a carrier's behalf, but it's rare, and even then the permit names the carrier and truck. As the broker or shipper, your job is to price the permits and verify they exist before the wheels turn.
- The permit specifies the route. Not "I-40 west," the actual roads. Deviate from the permitted route and the permit is void, along with the insurance story if anything happens.
- Most desks use a permit service. Around $39 per state standard, $65 complex. They file, chase approvals, and know each state's quirks. Filing direct with every DOT works, but it's a job.
- Wrong dimensions void the permit. If the load is bigger than the paper says, the fine is the least of the problem: the move is uninsured against the permit.
Escorts: pilot cars, pole cars, police
Past a certain size the load can't move alone. Three kinds of escort, three different jobs, three different prices. The triggers are state lines, and they vary more than any other rule in this guide.
Pilot car width & length
A civilian escort vehicle ahead or behind the load. Warns oncoming traffic, calls out obstructions, blocks lanes through pinch points.
One car typically from 12' wide; two cars from around 14'. Convention: the escort runs in front on two-lane roads, behind on divided highway.
Pole car height
A front escort carrying a flexible height pole set a few inches above load height. If the pole hits a wire or a bridge, the load stops before the cargo does.
Required for tall loads; the trigger height is state-set and spans more than four feet.
Police escort the wildcard
State troopers or county deputies, mandated by the DOT above certain sizes, most commonly 16'–20' wide.
Budget $200–$2,000 per state. The price is the officer's rate, often overtime, not a DOT fee schedule.
Escort cost, roughed in Interactive
Planning estimate at ~$1.90/mi pilot, ~$2.40/mi pole, day minimums applied at ~350 escorted miles/day. Escort quotes vary by corridor and season.
Route surveys
Above certain dimensions, someone has to physically drive the route before the load does: measuring bridges, wires, and turns with a tape measure and a notebook. States set the trigger; the spread is enormous.
What gets checked
- Bridge and underpass clearances, vertical and side
- Utility lines, traffic signals, sign gantries
- Turning radii at intersections and ramps
- Construction zones and active detours
- Railroad crossings, including wire heights
The facts
- Who does it: an escort or pilot-car company, not the DOT
- Cost: around $2/mi plus a $300 base; $750 minimum, $2,500 typical ceiling
- DOT engineering review adds $100–$500 where required
- Timing: it happens before the permit can issue, so it's on the critical path
Survey triggers by height: a five-and-a-half-foot spread
| State | Trigger | Note |
|---|---|---|
| New Hampshire | 13'6" | Strictest in the country: the legal limit itself |
| Massachusetts | 13'8" | Second strictest |
| CT, NY | 14'0" | Northeast cluster |
| MD, NJ, PA, VT, VA | 14'6" | Mid-Atlantic norm |
| Most states | 15'–16' | The default range; 13 states sit exactly at 16' |
| FL, TX, UT | 18'–19' | The lenient end; TX at 18'11" |
| GA, ID, KS, OK, RI, SD, WV, HI | none | No height trigger on the books |
Superloads: where routine ends
Every state draws a line where it stops stamping permits and starts engineering them. Cross it and the DOT reviews your specific load on your specific route: bridge analysis, mandated escorts, and a timeline measured in weeks.
Superloads change the process, the cast, and the money enough that they get their own guide: lead times by state, the bridge-analysis review, utility lifts, police mandates, and how to quote one without getting burned.
When the load can move
An oversize permit isn't permission to drive whenever. Most states restrict OD travel to daylight, many restrict weekends, and every one of them blacks out major holidays. Transit time is a calendar problem, not a mileage problem.
Holiday blackouts
Virtually every state bans OD travel on the big six: New Year's, Memorial Day, July 4th, Labor Day, Thanksgiving, Christmas. Most extend the blackout from noon the day before to sunrise the day after; some northeastern states add Good Friday or Easter. A holiday inside your transit window can cost two to three calendar days.
Urban curfews stack on top. Many metros bar OD moves through rush hours (California cities run roughly 6–9 AM and 3–6 PM), and Texas restricts superloads in the Houston and Dallas corridors overnight. Weather counts too: most states halt OD movement when visibility drops below about 1,000 feet. The permit lists the windows; read them.
Transit days, roughed in Interactive
Reading an OD quote
Every oversize quote is a stack. Price each layer on its own and the total defends itself; guess at the stack and the surprises come out of your side of the deal.
The checklist before you quote
- Get exact dimensions from the shipper, not rounded. 8'6" and 8'7" are different worlds.
- Ask for loaded height: cargo plus the deck it rides on, and overall length including overhang.
- Confirm the load is non-divisible.
- Count travel days against daylight windows, weekends, and holidays, not just miles.
- Anything over 14' tall or 100,000 lbs: verify the permit path before you commit a number.
The classic first-timer mistakes
- Measuring the cargo, not the ride. A 9' crate is legal in a warehouse and 14' tall on a flatbed. Height is measured ground to top of the loaded trailer.
- Trusting the spec sheet's "about." Dimensions on a purchase order are routinely wrong. The cheapest insurance in heavy haul is a tape measure on the loaded truck before the driver leaves origin.
- Quoting miles, not days. Daylight-only pace is the schedule, and detention math follows it.
- Assuming the weekend. Eight states restrict it; holiday weekends stall a load for days.
- Skipping the escort call. Escort availability is a real constraint in rural corridors; book early.
Talk the language
The vocabulary that gets used on the phone.