A freight-train derailment two years ago on the Union Pacific Bridge over Tempe Town Lake that spawned fires and a hazardous-chemical spill was caused by a broken rail, the National Transportation Safety Board said in its report of the incident released June 9.
Twelve of the train’s 97 cars jumped the track at about 6 a.m. on July 29, 2020, destroying a section at the southern end of the 110-year-old bridge.
One of the derailed cars struck the bridge structure, and part of the bridge collapsed, dropping railcars and bridge structure onto Rio Salado Parkway below and temporarily shutting down the road.
One of the derailed cars carried 2,200 gallons of cyclohexanone, a flammable liquid, that ruptured. The hazardous chemical did not spill into Town Lake but it puddled below the bridge and some seeped into a storm drain that feeds into the Salt River.
Arizona Department of Environmental Quality investigated, conducting 70 tests, and concluded that no further cleanup was necessary.
Other derailed cars carried lumber, which ignited into a massive blaze on the bridge. One firefighter was treated for smoke inhalation.
In its completed investigation, the NTSB placed probable cause of the derailment and bridge collapse on a broken rail located on the ballast deck portion of the wooden trestle approach to the bridge.
The incident likely was made more severe, the report says, due to there being no inner guard rail along the approach, in turn allowing derailed cars to move laterally into the bridge structure, causing its collapse.
View full NTSB report here.
First responders from four cities battled the ensuing fire and assisted in removal of hazardous materials. Tempe also sent engineers, water-quality experts and municipal utilities workers.
The city issued a statement on the NTSB findings, commending “the thorough investigation.”
Union Pacific has reimbursed Tempe $481,715 for expenses related to the derailment, which includes repair and replacement of damaged city property (portions of Rio Salado Parkway and Tempe Beach Park trees, streetlights and hardscape), incident-response costs, traffic control and environmental testing.
The railroad also spent approximately $11 million to repair and replace portions of the historic bridge damaged by the derailment and fire.