When Andy Pate’s GMC Sierra pickup hit the southbound Causeway’s right-side guard rail May 31, it sailed into the air as if the railing was a “ ‘Dukes of Hazzard’ ramp,” he said, plunging the 26-year-old into the waters of Lake Pontchartrain some 25 feet below.

Pate was able to use his elbow to knock out the driver’s side window and swim to the surface, where he was rescued by a motorist driving behind him who saw what happened and leaped into the lake to help. The entire event took place so quickly that Pate hardly had time to think. But he does remember assuming his truck would hit the railing and then bounce back into traffic.

“The guardrail had no protection at all,” he said. “It acted as a ramp.”

Pate was more fortunate than Miguel Rodriguez, whose Ford F-250 did almost the exact same thing last fall — hitting the inside barrier, then swerving to the outside and back to the inside before going over the railing and off the southbound span. After initially surfacing and telling someone he was all right, Rodriguez slipped underwater. His body was found the next day.

Since 1995, 11 vehicles have gone off the Causeway and into Lake Pontchartrain. The rate seems to be increasing: There have been four in the last two years, including two fatalities. All of the accidents have happened on the southbound span, where the barriers are 6 inches lower than on the northbound side.

A railing that sits atop the southbound barrier was designed as a handrail and offers little to no protection for cars. That, in addition to the increasing prevalence of high center-of-gravity vehicles, such as pickup trucks and sport utility vehicles, is a major source of concern to Causeway officials, who last fall commissioned engineers at Texas A&M’s Transportation Institute to study ways to improve safety on the southbound span in a cost-effective manner.

The analytic part of the study has been completed, according to Carlton Dufrechou, general manager of the Greater New Orleans Causeway Commission, which operates the bridge. Testing on three new barrier designs was supposed to begin later this month, but delays in fabricating the parts have pushed it back by a couple of weeks, Dufrechou said.

The testing is now slated to begin in mid-July on the bridge’s old 9-mile turnaround, which is no longer used. Workers will attach the railings and then test them to see if they can take enough force to move to the next stage of testing.

Two of the models to be tested involve a double railing that would add 21 inches to the barrier height. The third is a single rail that would increase the height by 12 inches. The designs also will be tested at an airfield used by the Transportation Institute in Texas, where actual vehicles will be crashed into them to determine their performance. If all goes as expected, the engineers will recommend one of the designs to the Causeway Commission.

William Williams, a research engineer at the Transportation Institute whose specialty is retrofitting old bridges with new railings, said the Causeway’s issue is not uncommon. Bridges are built to fit the type of cars being used at the time — the southbound Causeway was built in 1956 — and the vehicles outgrew the railings, he said.

Williams, who helped retrofit the U.S. 11 bridge between Slidell and New Orleans, said the Causeway’s existing concrete barrier, at 25 inches, should provide enough of a base to mount new barriers on top of it.

Once a recommendation is made, however, the Causeway Commission will have to find a way to fund it, by either obtaining grants or raising tolls. The cost of the rails would likely pale in comparison to another safety feature officials would like: putting pullover bays between each of the bridge’s seven crossings.

Adding the 12 bays — six on each side — would triple the amount of emergency stopping space on the bridge, Dufrechou said. But the price for such work is steep: probably $50 million or $60 million, he said. It would be worth it, bridge officials say, because between eight and 10 cars break down per day on the Causeway, creating delays and potentially dangerous situations in areas where there is no room to move a car off the road.

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