Broken Rail Caused 2020 Tempe Train Derailment, Bridge Collapse: NTSB

TEMPE, AZ —The National Transportation Safety Board (NTSB) released an investigative report Thursday that said a broken rail likely was the cause of the July 2020 freight train derailment and bridge collapse over Tempe Town Lake.

The fiery derailment involved 12 of the train's 97 cars and caused a partial collapse of the Salt River Union Pacific Bridge, which was built in 1912. Several cars carrying hazardous materials overturned, leaking chemicals into the area.

There were no fatalities, though one firefighter was treated for smoke inhalation at the scene, according to the NTSB.

The NTSB's 9-page report titled "Union Pacific Railroad Derailment with Bridge Strike and Fire"
detailed the facts of the derailment — which the agency gathered during a lengthy investigation — before explaining the "probable cause " of the incident.

"The probable cause of the Union Pacific Railroad freight train derailment and subsequent bridge collapse on July 29, 2020, was a broken rail located on the ballast deck portion of the wooden trestle approach about 30 feet from the steel bridge," the NTSB wrote. "Contributing to the severity of the derailment was the absence of an inner guard rail preceding the steel bridge structure, which allowed the derailed equipment to move laterally into the bridge structure and cause its collapse."

According to the report, the derailment occurred at 6:06 a.m., and the train was not traveling too fast, remaining in compliance with the 25-mph speed restriction on the bridge.

Five of the 12 cars that derailed were tankers carrying various hazardous materials. One of the tankers released about 2,200 gallons of cyclohexanone, a flammable liquid that created a pool of hazardous material below the damaged bridge, the NTSB said.

The report also said that Union Pacific estimated the cost of the derailment to be about $11 million, including $485,000 for railroad equipment, $435,000 for track and structures and $10 million for the bridge.