The National Transportation Safety Board said Tuesday that it would investigate a massive crash last week involving more than 130 vehicles on an icy Fort Worth highway that killed six people and injured dozens more.
The NTSB said on Twitter that its safety investigation would focus on snow and ice treatment procedures used on the highway.
The crash last Thursday on Interstate 35W north of downtown Fort Worth left a tangle of 133 semitrailers, cars and trucks smashed and tangled with one another, with some vehicles tossed onto others and drivers trapped.
The crash happened about 6 a.m. Thursday as many hospital and emergency workers were heading to and from work, so some of those involved were health care workers, police officers and other emergency responders, officials said.
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The NTSB said it's coordinating with the North Tarrant Express and the Texas Department of Transportation on the investigation.