"On any given weekend we probably average at least one freeway closure"
Houston Assistant Police Chief John Trevino says more often than not fatal accidents are caused by a drunk driver. Investigators are then faced with a crime scene. They have to gather evidence for felony cases that could be as serious as intoxication manslaughter. Trevino says the process usually takes two to three hours.
"And each crash, or each fatality accident is unique and different. How large the accident is and how many variables are involved will determine how long we actually have to have the freeway closed."
Trevino says HPD sends a team of six accident investigators. Other officers block off the freeway.
They set up two separate barricades to ensure investigators' safety as traffic is detoured off the freeway. A prosecutor from the District Attorney's Office also reports to the scene.
If the wreck involves an eighteen-wheeler or a fuel spill the shutdown could last even longer.
"Sometimes TxDot comes out and actually has to do an assessment of how much damage was actually done to the freeway."
Trevino says like any crime scene, it's crucial to gather evidence quickly.
Troy Walden studies freeway crashes for the Texas Transportation Institute. He says if freeways stayed open during accident investigations it would be much more difficult for police to figure out what happened.
"For instance you have short-lived evidence such as your skid marks and debris patterns such as glass patterns that are spread across the roadway surfaces, fluid transfer. And all those things are very short-lived evidence. And in order to be able to capture that, we have to shut it down so that other cars don't run through and disrupt the patterns and eradicate a lot of the evidence."
Houston police say if there's a high-profile accident they may have to shut down the freeway a second time for more investigation. But they try to do that at a time when there's the least inconvenience to drivers.
This story first aired October 5, 2011.