Bridge Clearance Safety: Avoiding Overheight Strikes and Route Planning

The Consequences of Bridge Strikes

Bridge strikes by commercial vehicles are more common and more dangerous than most drivers realize. Approximately 15,000 bridge strikes occur annually in the United States, causing millions of dollars in infrastructure damage, cargo loss, traffic disruption, and occasionally injuries and fatalities. A single bridge strike can cost $100,000 to $500,000 in bridge repair, plus the cost of the damaged truck, destroyed cargo, and traffic management.

The legal consequences are severe. Bridge strikes result in citations for the driver, carrier liability for infrastructure damage, potential criminal charges if injuries occur, and negative impact on the carrier's CSA score and insurance rates. Some states pursue civil recovery of bridge repair costs from the driver and carrier, which can amount to hundreds of thousands of dollars.

Bridge damage from a strike may not be visible from the road surface. An impact that appears minor can crack structural beams, shift bearing pads, and weaken the bridge's load-bearing capacity. Bridges struck by trucks must be inspected before being reopened to traffic, often requiring lane closures for hours or days. You are legally required to report any bridge strike to the authorities immediately.

Knowing Your Vehicle Height

Know your total vehicle height including any roof-mounted equipment. A standard dry van trailer measures 13 feet 6 inches from the road surface to the top of the trailer. A reefer trailer with the refrigeration unit on top may measure 13 feet 8 inches to 13 feet 10 inches. A flatbed loaded with tall freight may exceed standard heights.

Dynamic height changes affect your clearance. Air ride suspension at full inflation adds height compared to when the truck is parked and the suspension has settled. Driving over a bump can momentarily extend the suspension, adding 1 to 2 inches to your height. Temperature changes can affect tire inflation, changing overall height slightly. These variations mean you need more than the minimum posted clearance.

Post your vehicle height in the cab where you can see it constantly. Many fleets require a height sticker on the dashboard, sun visor, or headliner. Knowing your height without having to think about it means you can instantly compare it to any clearance posting you encounter.

Verify height after any change to the vehicle or load. New tires (different overall diameter), different trailer (reefer vs dry van vs flatbed), tall cargo on a flatbed, or roof-mounted equipment changes all affect total height. Remeasure and update your height reference whenever the configuration changes.

Route Planning for Height Clearance

Commercial GPS navigation systems (Garmin Dezl, Rand McNally, TruckMap, Trucker Path) include bridge height data and route around low clearances when programmed with your vehicle dimensions. Always enter your exact vehicle height into the GPS. Using car GPS or consumer navigation apps that do not account for bridge heights is one of the most common causes of bridge strikes.

Pre-trip route planning should identify any bridges, underpasses, and tunnels on your route and verify their clearance heights. Many states publish lists of low-clearance bridges online. The FHWA National Bridge Inventory includes height data for most bridges. For unfamiliar routes, verify clearances before departure rather than discovering a low bridge while driving.

Local knowledge is invaluable for regular routes. If you run the same lanes repeatedly, you know every bridge on the route. But detours, construction, and new routes introduce unfamiliar infrastructure. When your GPS routes you off your normal path, be especially vigilant about clearance signs because the detour route may include restrictions your regular route does not.

When delivering to locations with parking garages, loading docks under buildings, or covered entrances, verify the facility's clearance before entering. Many distribution centers, shopping center loading docks, and industrial facilities have overhangs or structures that are lower than standard highway bridges. Ask the receiving facility about clearance heights when confirming your delivery appointment.

Recognizing and Responding to Low Clearance Warnings

Standard yellow diamond low clearance signs display the bridge clearance height. These signs are posted in advance of the bridge to allow trucks to stop and turn around. The sign may show the clearance in feet and inches (for example, 12 feet 6 inches) or as a single number. Some signs include a secondary sign indicating the clearance of an alternate route.

Overheight detection systems at some low bridges include sensors that detect approaching vehicles exceeding the clearance height. These systems activate flashing lights, warning signs, and sometimes physical barriers to alert the driver. If you trigger an overheight warning, stop immediately and do not proceed. The warning system is telling you that your vehicle will strike the bridge.

Posted clearance heights include a safety margin, typically 3 to 6 inches below the actual structural clearance. A bridge posted at 13 feet 6 inches may have an actual structural clearance of 13 feet 9 inches to 14 feet. However, never rely on this safety margin as your clearance buffer. Road repaving raises the road surface and reduces actual clearance. Winter snow accumulation on the bridge structure reduces clearance. Vehicle bounce and suspension dynamics change your height momentarily.

If you are uncertain about clearance, stop before the bridge and assess. It is always better to stop, get out, and look than to damage a bridge. If you determine the clearance is insufficient, do not attempt to back up on a highway. Use a safe turnaround point, which may require traveling past the bridge to find one.

What to Do If You Strike a Bridge

If you strike a bridge, stop immediately in a safe location past the bridge (do not stop under the damaged structure). Turn on hazard flashers, set out warning triangles, and call 911 to report the strike. You are legally required to report the incident regardless of how minor the contact appeared.

Do not continue driving. Your trailer may have structural damage that is not visible from the cab, including roof punctures that expose cargo to weather, structural deformation that makes the trailer unsafe for loading, and roof-mounted equipment (reefer units, air deflectors) that may be damaged or partially detached.

Document the incident thoroughly. Photograph the bridge (including the clearance sign and any visible damage), photograph your vehicle damage, note your exact location, the posted clearance height, your measured vehicle height, and the time and conditions. This documentation is essential for the incident report, insurance claim, and any legal proceedings.

Notify your carrier immediately. The carrier's safety department will guide you through the reporting process, arrange for vehicle inspection and towing if needed, and coordinate with their insurance company. Do not leave the scene until instructed by law enforcement or your carrier's safety team.

A bridge strike investigation will examine whether you were on an approved truck route, whether your GPS was programmed with correct vehicle dimensions, whether you disregarded posted warning signs, and whether you had proper documentation of your vehicle height. Having correct answers to all these questions demonstrates that the incident was an anomaly rather than negligence.