Over the road commercial trucks deliver products to and from manufacturers, warehouses and retailers across the country's extensive highway system. These commercial vehicles are regulated by federal, state and local agencies. Commercial over the road (OTR) truck drivers must be aware of different regulations, as well as the size of their rig and any limiting factors, such as low bridges, that they may encounter along their route.

Clearly Marked Height

Most tractor-trailer rigs have the trailer's height clearly marked on the leading edge of the trailer. The markings are painted in reverse so that when the OTR driver looks in his rear view mirror, the label is viewed in the proper orientation. As the commercial driver travels down the highway, every overhead bridge has a roadside sign that clearly announces the bridge height. Drivers must be aware of their truck's height and the height of oncoming bridges at all times. The trailer's height is visible in the rear view mirror at the driver's eye level.

Federal Height Regulations

While the federal government regulates most aspects of commercial semi-truck drivers and their equipment, it has not imposed a federal vehicle height limit. However, the height of existing bridges serves to limit the height of trucks and trailers that can safely pass under them. A semi rig and its trailer must be a lower height than the measured bridge clearance.

State Height Regulations

Local and state transportation agencies impose height limitations for commercial semi-tractor trailer trucks. Most states have limited commercial semi rigs to a height of 13 feet, 6 inches. Some states allow a vehicle's height to reach 14 feet, such as Florida's regulation for car-carrying vehicles. Colorado allows a maximum height of 14 feet 6 inches. States issue local regulations as a way of protecting the commercial OTR driver. Because states track the height of the bridges in their jurisdiction, their guidelines let the truck drivers know the maximum size trailers that can travel through their states.

Low Clearance Bridges

In some cases, the geographic formations in or around a highway's construction path limited a bridge height. In this case, state highways are clearly marked with a “Low Bridge” clearance sign, so unsuspecting drivers can exit the highway before encountering a low bridge. Serious injury to the truck driver, cargo and the highway bridge can occur if an OTR semi driver fails to identify a low bridge hazard.