Bridge Clearance and Height Restrictions for Oversize Loads

Federal Height Limits: There Aren't Any (Sort Of)

Here's a fact that surprises many shippers: there is no federal maximum height limit for commercial vehicles. Unlike gross vehicle weight (80,000 lbs), axle weights (20,000 lbs single / 34,000 lbs tandem), and width (8'6"), height is regulated entirely at the state level. States set their own height limits, which typically range from 13'6" to 14'6" depending on the state.

The practical implication: a load that is legal height in one state may be overheight in the next. Your carrier must know the height limit for every state on the route and obtain overheight permits where required.

State Height Limits: The Patchwork Problem

Most states set their standard height limit at 13'6" or 14'. A few states allow 14'6". Here's why this matters in practice:

• A 14'2" load is legal in states with a 14'6" limit but requires an overheight permit in states with a 13'6" or 14' limit
• Multi-state moves require permits from every state where the load exceeds that state's limit
• Some states have different height limits for different road types (interstate vs. state highway vs. county road)
• Urban areas often have lower clearances than rural interstates due to older infrastructure

The solution: always measure your load's total height (equipment height + trailer deck height) before booking transport, and share that measurement with your carrier so they can identify which states require overheight permits.

How Bridge Clearances Are Determined

Bridge clearance is the vertical distance between the road surface and the lowest point of the bridge structure above. The Federal Highway Administration (FHWA) requires that bridges on the Interstate Highway System provide a minimum clearance of 16 feet. However, many older bridges — particularly on state highways, county roads, and urban streets — have clearances as low as 11'–13'.

Bridge clearance data is maintained by state DOTs and is available through permit routing systems. When you apply for an overheight permit, the state's routing system automatically identifies bridges on the proposed route that may be too low for your load and either flags them for manual review or routes you around them.

The Height Pole: Your First Line of Defense

For overheight loads, the lead escort vehicle is equipped with a height pole — a rigid pole or cable extended to the permitted height of the load. As the escort vehicle travels ahead of the transport, the height pole physically contacts any overhead obstacle that is lower than the load's permitted height, giving the driver time to stop before the transport vehicle reaches the obstacle.

Height poles are required by most states for overheight loads. They are a critical safety device, but they are not foolproof:

• The height pole must be set to the correct height — the actual height of the load, not the permitted height
• The escort vehicle must maintain adequate lead distance to give the transport driver time to stop
• Height poles do not protect against overhead power lines, which can be more dangerous than bridge strikes
• Overhead power lines require coordination with utility companies for temporary de-energization or raising

Common Scenarios That Create Height Problems

Equipment on Lowboy Trailers

Even a lowboy trailer adds 18–24 inches to the equipment's height. A 12' tall excavator on a 20" deck lowboy is 13'8" total — overheight in states with a 13'6" limit. Always add trailer deck height to equipment height when calculating total transport height.

Equipment with Raised Components

Booms, masts, antennas, and other raised components must be lowered or removed before transport. A telehandler with its boom raised is obviously too tall, but even a "lowered" boom may add unexpected height. Verify the transport configuration height, not the operating height.

Rail Cars and Intermodal Containers

Rail cars and ISO containers are particularly challenging because they are tall by design. A standard 40' ISO container (9'6" tall) on a lowboy trailer results in a combined height of approximately 11'–11'6" — legal in most states. But a high-cube container (10'6" tall) on the same trailer is 12'–12'6", which may require permits in some jurisdictions.

Urban and Industrial Areas

Urban areas have the highest concentration of low clearances: railroad overpasses, utility bridges, parking garage entrances, and older highway structures. Overheight loads in urban areas require the most careful route planning and often require nighttime travel to minimize traffic disruption during slow-speed navigation around obstacles.

What Happens If You Hit a Bridge

Bridge strikes have serious consequences:

• Criminal liability: Driving an overheight load into a bridge without a permit is a criminal offense in most states, with fines ranging from $1,000 to $25,000+
• Civil liability: The carrier and shipper are jointly liable for bridge repair costs, which can run into the millions of dollars for structural damage
• Load damage: The load is almost always destroyed or severely damaged in a bridge strike
• Traffic disruption: Bridge strikes often close major roads for hours or days while structural engineers assess damage
• Insurance consequences: Bridge strikes can result in policy cancellation and difficulty obtaining future coverage

How IronHaul Plans Around Height Restrictions

IronHaul Logistics uses state permit routing systems and proprietary route planning tools to identify and avoid low clearances on every overheight move. Our process includes:

1. Collecting exact load height from the shipper (equipment height + trailer deck height)
2. Running the route through state permit systems to identify low bridges
3. Selecting alternate routes around low clearances when necessary
4. Coordinating with utility companies for overhead power line clearances
5. Briefing the driver and escort team on specific clearance points along the route
6. Equipping the lead escort with a properly calibrated height pole

If you're shipping tall equipment and want to make sure your move is planned correctly, call IronHaul Logistics at (208) 495-2260, email [email protected], or submit a quote request online. We handle overheight route planning as part of every permitted move.