A broken rail derailed hauling coal in Colorado as it passed over an interstate highway over the weekend, early investigations show.

sent 30 railcars off the tracks, collapsing the steel bridge on top of a passing tractor-trailer, crushing the cab and killing the 60-year-old driver inside. are now examining the fatal incident and why it happened despite the warning systems in place.

The fatal derailment last Sunday left a nine-mile stretch of Interstate 25 closed near Pueblo, Colorado, according to The closure is expected to last the next few days as the bridge’s wreckage, crumpled railcars and tons of coals still block the roadway. While assessing the bridge and highway damage will be a priority once the debris is cleared, investigators will look into how the systems in place to prevent derailments like this failed.

The NTSB has long recommended that railroads install more automatic monitoring systems that can detect problems with tracks early on and prevent accidents. The agency repeated its call for those systems in July in response to a fatal Amtrak derailment along BNSF-owned tracks in northern Montana two years ago.

It was not immediately known whether the track where Sunday’s derailment occurred had such a system. NTSB spokesperson Sarah Taylor Sulick said that was part of the investigation.

“They will be pulling maintenance records. They’ll be interviewing people involved. They’ll be talking to the railroad. They’ll be talking to the state,” Sulick said.

BNSF has not said when it last conducted an inspection and did not immediately respond to emailed questions or requests to view its inspection records.

Former NTSB investigator Russell Quimby said an automatic warning system likely was in place in Colorado because the accident happened along one of the railway’s main routes between Denver and Texas, where BNSF is headquartered and which has numerous coal-burning power plants.

It will be vital for investigators to determine precisely when the rail broke. If the track came apart when the train was traveling over it, then there was nothing the crew could’ve done to avoid the derailment. If not, then the focus will shift toward All possibilities for a cause are still on the table including intentional sabotage and vandalism.

Train derailments have been in the national spotlight since earlier this year. The spotlight has shown a myriad of systemic issues However, the increased scrutiny from regulators and the media hitting the ground.