Adding a steel rail atop the concrete barriers that line both spans of the Lake Pontchartrain Causeway would make the bridge safer, a Texas A&M engineer told a Mandeville audience Wednesday night.

The present barriers, especially the 25-inch-high ones on the southbound bridge, are too low to prevent high-profile vehicles, such as trucks and SUVs, from vaulting over the edge like “a ‘Dukes of Hazzard’ ramp,” as one driver described it.

A double steel rail, bolted into the concrete barrier and rising nearly 2 feet above it, would greatly improve the chances of keeping cars and trucks on the bridge when they lose control and begin swerving, according to engineer William Williams.

Williams made a similar presentation at a Greater New Orleans Expressway Commission meeting earlier this year.

The GNOEC commissioned the Texas A&M study as a way to help prevent “overboards,” crashes in which a vehicle goes over the side of the bridge into Lake Pontchartrain. Since 1994, there have been about 14 overboards on the Causeway, 11 of which have resulted in fatalities.

All but one of the 14 occurred on the southbound span, where the concrete railings are 6 inches lower than on the northbound bridge. The metal rail on top of the barrier on the southbound bridge is only a handrail and provides no resistance to cars that hit the barrier, according to Williams, who headed the study.

The difference between the two bridges’ railings — built a decade apart in the last century — was brought into sharp relief Wednesday morning, when a northbound 18-wheeler swerved and slammed on the brakes in an effort to avoid a slower-moving car, said Carlton Dufrechou, the GNOEC’s general manager.

Partially due to the higher railings on the northbound span, the truck did not go overboard but stopped with one tire overhanging the barrier, Dufrechou said.

Williams and his team tested four different railing designs. Two of the designs had a single rail and two had double rails. They crashed three different vehicles into each of the railings, judging each on impact and how well it kept the vehicle in the roadway.

The double rail performed the best, Williams told his audience of several dozen Wednesday night. Putting it on top of the concrete barrier on the southbound span would raise the barrier height to 46 inches.

At that height, Williams said, the rail should be able to prevent most large vehicles, including large panel trucks, from going over the side. A single rail on top of the northbound bridge’s concrete barrier would be sufficient, he said.

Some in the audience questioned whether people driving on the bridge would still be able to see the lake and whether keeping out-of-control cars on the bridge would be less safe for other drivers.

Dufrechou said the possibility of saving someone’s life diminishes “astronomically” if they go over the side.

The Causeway’s engineering consulting firm, GEC, is conducting a study of the cost of installing nearly 100 miles of railings on the bridge. The results are expected in September or October.

It will likely be next spring before the timeline for any project could be established, Dufrechou said.

The true challenge will be footing the bill, which could reach nine digits. Causeway officials have been unsuccessful in securing federal grants for the project, but they have vowed to keep trying. They have also floated the idea of raising tolls on the bridge, which have gone up just one time in the bridge’s nearly six-decade history.

Follow Faimon A. Roberts III on Twitter, @faimon.