BNSF Railway says its workers inspected a stretch of track north of Pueblo within hours of when one of the rails is believed to have broken, causing a deadly train derailment and bridge collapse.

The company, which owns the train and the segment of track it was running on, said this week that it used a combination of techniques to test the track in the months and hours before Sunday afternoon’s derailment. The disclosure in response to media questions comes as federal officials are investigating the crash, which killed a truck driver and closed Interstate 25 for several days after a rail bridge collapsed onto the highway.

BNSF’s communications staff did not provide detail on the exact timing of the inspections, but Lena Kent, the railway’s general director of public affairs, said Wednesday that the most recent inspection of the track section occurred Sunday prior to the incident.

On Tuesday, investigators with the National Transportation Safety Board said they believe the crash was caused by a broken rail on the track just east of the I-25 bridge — a failure that one expert said normally is caught by detection equipment “99.99%” of the time.

“Nothing is 100%,” said Allan Zarembski, the director of the University of Delaware’s Railway Engineering and Safety Program.

He said the ultrasonic equipment used to test and look for rail breaks is the industry standard and state of the art. “When you’re in the 99.9% or 99.99% success rate, it’s really, really difficult to pick up those outliers.”

Railroads identify roughly 200,000 broken rails every year, Zarembski said, and there are usually 60 to 80 derailments caused by broken rails annually. The rails typically break because of “internal fatigue,” he said, the result of steel bearing “millions and millions” of loads.

It’s a serious issue, he said, though railroads “tend to do a very effective job” of identifying and fixing them.

Still, inspections — like those using ultrasonic detection methods — can miss the breaks if they’re too small or if there’s something on top of the rail blocking the detection.

Thirty of the BNSF train’s 124 cars derailed Sunday, spilling coal and debris across the interstate and likely triggering the bridge collapse that killed 60-year-old truck driver Lafollette Henderson, the NTSB said.

The NTSB’s derailment investigation may not conclude for a year or two, agency officials said this week, and the agency may not confirm the cause until that work is finished. But investigators are expected to issue a preliminary report in the coming weeks.

Generally speaking, Zarembski said, the moment when broken rails fail is often while a train is on top of them.

“It’s not unusual to have a broken rail under a train going at full speed. And when that happens, there can be a lot of damage,” he said.

I-25 was open in both directions as of late Thursday afternoon, after a partial reopening of the southbound side Wednesday.

Though the derailment happened Sunday, throughout the week state and railroad officials were sorting out who owned the collapsed bridge, which was built in 1958, and who had ultimate authority for its maintenance.

Zarembski, the University of Delaware expert, said he’d never seen such ownership confusion before.

“It’s the first time I’ve heard of it,” he said. “I’ve never heard of a situation where nobody knows who owns the bridge.”

A spokeswoman for the NTSB previously told the Post that the bridge didn’t have a name. It also doesn’t appear in publicly available federal bridge records. On Wednesday, Colorado Department of Transportation spokesman Matt Inzeo identified the bridge by its official designation.

It does appear in state records, where its condition is rated as “poor,” and Inzeo said it was not part of a federal schedule of bridges requiring regular state inspection. But CDOT confirmed that the state inspected the structure in 2022. The Post has requested records from that and other state-run inspections, though Inzeo said they may not be released until after the NTSB completes its investigation.

The state and the railroad appear to have decided on a path forward: Spokespeople for CDOT and BNSF told The Denver Post that the railway would assume responsibility for replacing the bridge.

“I can confirm that BNSF does have responsibility for inspections and maintenance of the structure and will be replacing the bridge,” Kent from BNSF said in an email.

The railway will continue handling inspections and maintenance of the bridge once it’s replaced, CDOT’s Inzeo said.