On a number of occasions, truck drivers have found themselves trapped in a scenario where there are two bridges, one right after another, and  the truck can fit under the first but not the second bridge, without an exit in between. This led to drivers striking bridges. District and maintenance engineers at the Texas Department of Transportation (TxDOT) expressed concerns that new construction, such as reverse-diamond interchanges, would lead to more safety problems if the issue was not addressed. Texas A&M Transportation Institute researchers were asked to research ways to better communicate low-bridge warnings to truck drivers now and in the future.

 

The first step was to brainstorm different types of warning signs that would draw truckers’ attention to the fact that they would need to exit before the first bridge in order to avoid being trapped on the freeway after approaching the second, lower bridge. Signs would need to be added to the freeway to encourage truckers to exit, as well as on the frontage road to discourage truckers from approaching a bridge they could not fit under.

 

Six freeway signs and two frontage road signs were chosen for a survey of commercial truck drivers.

 

After viewing each sign, drivers were asked if they interpreted the following information from the sign:

• there is no exit between bridges,

• there is no exit before the second bridge,

• you need to exit now if your truck is taller than the sign dimensions, and

• the information on the sign shown is not for the first bridge.

 

A greater percentage of participants responded positively to a warning sign similar to current low-bridge warning signs that included subsidiary information saying “2nd bridge, exit now,” as well as a green sign that stated “last exit before” and displayed an image of the typical low-bridge warning sign.

 

After the surveys, researchers prepared a simulator to further test six of the signs. Before going into the simulator, some signs were removed due to their differences from the Manual on Uniform Traffic Control Devices standards. Laura Higgins, co-principal investigator, said the researchers were concerned that nonstandard signs would confuse the drivers, which would distract them from actually reading the sign. Researchers also received feedback from TxDOT district engineers.

 

The simulator placed the drivers in the far left lane of a freeway. They were briefed beforehand about the characteristics and measurements of their vehicle. Each test included a distraction sign, such as a sign for an upcoming rest area, followed by the clearance test sign. Researchers were able to measure how much time passed before a driver began to move lanes in order to exit after viewing the test sign. Other truckers in the simulation were placed on the frontage road and were tested with a sign warning them not to enter the freeway.