With each call from an engineer Wednesday morning, pressure on a steel post attached to a concrete railing on the Lake Pontchartrain Causeway increased.

Before pressure applied by a hydraulic ram reached 24,000 pounds, a large pop was heard. When it reached 27,000 pounds, there was a louder pop accompanied by two large cracks that snaked out from the bolts that attached the post to its concrete base.

The cracks signaled the end of the test on the fourth of six posts due to be tested this week on the Causeway. The tests, conducted by Texas A&M’s Transportation Institute, are checking three different posts designed to be attached to the top of the 25-inch-high concrete railing on the southbound span of the 24-mile-long bridge. Currently, only a handrail sits atop the railing, and over the past two years, four vehicles have plunged into the lake off the southbound span, resulting in two fatalities.

The southbound bridge, the older of the two spans, was built in 1956. In the nearly six decades since then, cars have outgrown the low railing and the handrail, according to William Williams, a research engineer with the Transportation Institute. Since 1995, 11 cars have gone off the Causeway, all of them on the southbound side.

Last month, Andy Pate, who was driving a GMC Sierra pickup, hit the inside rail, then swerved to the right. The concrete curb and rail acted like a “ ‘Dukes of Hazzard’ ramp,” he said, vaulting his car into the air before it plunged 25 feet into Lake Pontchartrain.

Pate was lucky — he managed to surface and was assisted by a passing motorist who saw what happened and jumped into the water to help — but others haven’t been. In the fall, Miguel Rodriguez went over the side in his Ford F-250 pickup. After surfacing and saying he was all right, Rodriguez slipped back under and drowned.

Engineers from the Transportation Institute have constructed prototypes of three designs they are testing this week at the bridge’s old 9-mile turnaround, which is no longer used. Two of the three would raise the level of the railing from the current 25 inches to 46 inches, well above the level on the northbound bridge, where the railing is 31 inches high. The third would raise the railing’s level to 37 inches.

The goal of each of the designs is the same: to keep swerving cars on the road, Williams said Wednesday.

Cary Bourgeois, a consulting engineer on the project, said the 27,000 pounds of force applied to the post Wednesday morning would be the equivalent of a large panel truck hitting it. Though the force was applied steadily and not in a sudden strike, like a fast-moving truck hitting the railing, the two were analogous, he said.

Once the tests are completed this week, engineers at Texas A&M will construct a replica of the Causeway’s concrete railing in Texas in December. Then they will put each of the three posts on top of it, along with the raised railing designs, and crash vehicles into them.

Once that is completed, the engineers will recommend one of the designs to the Greater New Orleans Expressway Commission, which will have to tackle the problem of finding money for the new railing, either through grants or possibly by raising tolls.

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