Legal trailer height limits by state generally run from 13 feet 6 inches to 14 feet, and there is no federal ceiling that overrides them. Congress regulated commercial vehicle length, width, and weight but left height to the states, so the number that applies to you depends entirely on where you’re driving. Most of the country sits at 13’6″; a cluster of states, mostly in the West, allow 14 feet. Anything above your state’s limit requires an oversize permit before the wheels move.
Why Limits Are Set by States, Not Washington
The Surface Transportation Assistance Act of 1982 gave the federal government authority over several commercial vehicle dimensions on the National Network of highways, which includes all interstates and certain designated routes. That law set minimum standards for length and width and established weight limits. Height was deliberately left out. The Federal Highway Administration confirms it directly: “There is no Federal vehicle height requirement for CMVs. Thus, States may set their own height restrictions.”1Federal Highway Administration. Federal Size Regulations for Commercial Motor Vehicles
The reason 13’6″ works as a safe default on interstates is bridge design, not statute. Federal highway design standards require a minimum vertical clearance of 16 feet on rural interstate sections and 14 feet on urban interstate routes.2Federal Highway Administration. Vertical Clearance on the Interstate System A vehicle at 13’6″ passes comfortably under both. That margin is why the number became the industry benchmark and why most state legislatures adopted it as their legal ceiling.
The 13’6″ vs. 14′ Split Across the Country
Most states cap vehicle height at 13 feet 6 inches. A meaningful number allow up to 14 feet, and the pattern roughly follows geography: states west of the Mississippi River tend to permit the taller limit, partly because newer infrastructure was built with more generous overhead clearance. States in the East and Midwest, where older bridges and tunnels are common, generally stay at 13’6″.1Federal Highway Administration. Federal Size Regulations for Commercial Motor Vehicles
If a trip crosses state lines, plan around the lowest ceiling you’ll cross. A rig that’s legal at 14 feet in one state becomes an overheight violation the moment it enters a 13’6″ state. Route-planning software built for commercial vehicles can flag these transitions, but check each state’s current regulations before you leave; shorthand summaries age quickly.
Posted Clearances Override the State Limit
A statewide maximum is a ceiling for your vehicle, not a guarantee about any particular road. Older parkways, historic routes, and certain urban corridors carry posted clearances well below 13’6″, in extreme cases as low as 7 feet. Those posted numbers always control. A load that’s legal under state law is still illegal, and will still hit the bridge, if the structure overhead is shorter than the vehicle.
Treat posted clearance signs as hard numbers. In practice, settling, repaving, and snow accumulation can make actual clearance slightly less than what the sign shows, so if you’re within a few inches of a posted clearance, find another route. Don’t follow another tall vehicle through a low bridge on the assumption that if they cleared it, you will. Their height and yours may not match.
Travel Trailers, RVs, and Boats
State height limits apply to all vehicles, not only commercial trucks. If you’re towing a travel trailer, hauling a boat, or driving a Class A motorhome, the same state ceilings apply. Most factory-built RVs come in around 13’6″, which sits right at the legal limit in most states. That figure often doesn’t include rooftop air conditioning units, vent covers, or satellite dishes, so the real height after accessories can creep above the limit without the owner realizing it.
Non-commercial drivers tend to underestimate the risk because they’ve never had to think about overhead clearance. A pickup truck clears every bridge without a thought. Hitch a 12-foot travel trailer behind it and parkway overpasses, gas station canopies, drive-through lanes, and parking garage entrances all turn into potential collisions. Measuring the full rig once and writing the number on a card stuck to the dashboard is the simplest precaution most people skip.
Measuring Your Rig Correctly
Your legal height is the distance from the ground to the absolute highest point on the vehicle or trailer, measured while the trailer is hitched to the tow vehicle on level pavement. Everything on top counts: air conditioning units, vent covers, exhaust stacks, antennas, roof racks, and any cargo above the roofline. If a tarp flaps a few inches above a secured load, that flapping tarp is your height.
A few variables catch people off guard:
- Suspension sag under a heavy load can lower your height, so an empty trailer riding on fresh springs sits higher than the same trailer loaded. If you’re close to the limit, measure in both conditions.
- Tire inflation changes frame height. Even 10 to 15 PSI above spec can add a noticeable fraction of an inch.
- Trailer pitch depends on the hitch point on the tow vehicle, so a trailer that measures 13’4″ sitting in your driveway may read differently once hitched. Always measure while connected.
Work out your worst-case height, meaning the tallest the rig could possibly be under any loading condition. If that number sits within a couple of inches of your state’s limit, treat the rig as if it’s already at the limit and plan accordingly. Truck-specific or RV-specific GPS apps that flag low bridges and restricted parkways are worth the money; standard car navigation ignores clearance entirely.
Oversize Height Permits When You’re Over the Limit
When the load exceeds the state’s legal height, you need an oversize permit before you move. Every state handles these through its department of transportation, and most offer online applications where you enter vehicle dimensions and the planned route. The agency either approves the route or assigns an alternate path that avoids low-clearance structures.
Single-trip permit fees vary widely. Some states charge as little as $5 to $15 for a basic oversize permit; others charge $40 to $65 or more depending on how far the load exceeds legal dimensions. Superloads, those exceeding roughly 16 feet in height, can run into the hundreds of dollars per trip and may require additional engineering review. Annual permits are available in many states for operators who regularly haul oversized loads, often at a meaningful discount over repeated single-trip permits.
The permit itself typically specifies the exact route, allowable travel hours (many states ban oversize movement at night or during rush hour), and whether escort vehicles are required. For height specifically, most states east of the Mississippi require a pilot car with a height-measuring pole once a load exceeds 13’6″, while western states often don’t trigger that requirement until 14 feet. Loads taller than roughly 14’6″ almost universally need at least one escort regardless of state. The permit spells all of this out, and you’re required to carry it in the vehicle during the trip.
What a Bridge Strike Actually Costs
Operating overheight without a permit is one of the more expensive violations on the road. Fines vary by state but commonly start at several hundred dollars and can climb into the thousands, especially when the violation involves property damage. Some states also impound the vehicle until the fine is paid or a bond is posted.
If the rig actually strikes a structure, the operator or their company is typically liable for the full cost: bridge inspection, structural repair, road surface restoration, traffic sign replacement, emergency response, and claims from other motorists affected by the closure. Repairs can run from tens of thousands of dollars for cosmetic damage to hundreds of thousands for structural work. When the strike closes a rail line running over or under the bridge, delay costs compound quickly.
Secondary consequences follow. Insurance premiums rise after a bridge strike claim. Commercial driving privileges can be suspended or revoked. If other motorists are injured by falling debris or the traffic disruption, personal injury liability adds another layer. The driver’s own insurer may decline to cover vehicle damage if the driver ignored posted clearance signs. Know your height, trust the posted signs, and when in doubt stop and find another route. A 20-minute detour is always cheaper than a bridge strike.