Here’s my column from the Sunday paper. If you’ve already read it elsewhere (like here), please skip on down to the comments below. Thanks.

As Roadguy noted in this column from last month, the see-through railings on the new 35W bridge are making some drivers nervous. The rails meet federal standards and are higher than the ones on the old bridge, but that didn’t impress numerous alert readers, including one named Martha:

I love all the rationalizations I’ve read from the people who designed/built the bridge. In the long run, who cares what the standards are for the rail … how about going the extra mile to prevent another disaster? I think even one potential accident is a disaster.

Martha also was skeptical that a less-than-3-foot railing would prevent a 13-foot-tall semi from going over the edge.

To understand how railings are chosen, I tracked down Roger Bligh, a roadside safety expert at the Texas Transportation Institute. He said that the important thing is not what the railings look like or even necessarily how high they are. It’s how they perform in crash tests.

The 35W railings are rated “Test Level 4″ (the highest rating is TL-6). That means a railing with that design or something very similar was tested by crashing a loaded pickup truck weighing more than 4,000 pounds into it at 62 miles per hour, Bligh said.

Such a vehicle was chosen, he said, because of its similarity in weight and size to many SUVs and vans on the road. The speed and angle of impact were selected after analyzing data from real-world crashes.

To pass such tests, Bligh said, the railing must not allow the pickup to crash through it or travel over it, and it should not cause the pickup to tip over after impact.

Railings are further evaluated by what happens to a vehicle’s passenger compartment in a crash, Bligh said. How deformed would the car become? Are there elements of the railing that would snag a vehicle?

TL-4 railings also have to keep smaller commercial trucks from going over or through, though those trucks would be allowed to tip over onto their sides on the roadway, he said.

Roadguy is guessing that Martha would prefer all bridges to have TL-5 railings, which are rated for semitrailer trucks, or maybe even TL-6, which are rated for tanker trucks. (One TL-6 railing that Bligh has seen was about 7 feet tall, he said.)

But Bligh said he’s heard of little demand for the higher-rated railings around the country. “We’re not really aware of a problem of a lot of large trucks running through our barriers,” he said. And if a vehicle weighs enough and is going fast enough, “no barrier is going to be impenetrable.”

This entry was posted on Sunday, March 29th, 2009 at 4:34 pm and is filed under Main. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.