Transportation officials will now look into why that guard rail didn’t keep the bus from falling.
TxDOT says the guard rail design on the South Loop probably dates back to the 1970’s. But research engineer William Williams with the Texas A&M Transportation Institute says that doesn’t necessarily mean it’s not as strong as the rails designed today.
Williams says most railings are specifically designed to keep cars from falling off an elevated roadway. But when rail designs are tested to see if they’re crashworthy, Williams says researchers don’t look at every scenario.
“We don’t evaluate the rails under extreme conditions,” says Williams. “The tested conditions under the specifications just don’t cover extreme cases.”
Williams didn’t address the specifics of Tuesday’s accident, but as for why railings break, he says a lot depends on the angle of impact.
“If the angle is very steep obviously the load and the force on the rail is going to be greater,” says Williams.
TxDOT declined to make anyone available for an interview. In a statement, the agency says most bridge railings in the Houston district range between 36 and 42 inches.
TxDOT says it inspects bridges every two years, and the bridge at Telephone Road was last inspected in 2014. Officials say they’re now planning an extensive review of the bridge and others with similar guard rail designs.
The crash is also being investigated by the NTSB.