NTSB: Overstress, broken rail determined as the main causes in Tempe train derailment

Records from Union Pacific showed the company had removed the guard rail in the derailment area after a previous train derailed on the same bridge a few weeks
Published: Jun. 9, 2022 at 2:05 PM MST
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PHOENIX (3TV/CBS 5) - The National Transportation Safety Board (NTSB) released its final report regarding a train derailment and bridge collapse over Tempe Town Lake. A Union Pacific freight train derailed on the bridge while attempting to cross over Tempe Town Lake on July 29, 2020. Investigators said a broken rail caused the derailment. They also said the absence of an inner guard rail caused those derailed cars to crash into the bridge structure.

The derailment happened when a westbound Union Pacific Railroad freight train derailed while crossing the bridge over Tempe Town Lake, causing several cars to crash into the bridge structure, which investigators believe led to the partial collapse. Records from Union Pacific showed the company had removed the guard rail in the derailment area after a previous train derailed on the same bridge a few weeks before this catastrophic accident. Union Pacific told NTSB investigators the guardrail was under repair after the first derailment.

The derailment happened when a westbound Union Pacific railroad freight train was traveling over Tempe Town Lake just after 6 a.m. on July 29, 2020.

The missing guardrail

The guardrails installed on tracks work theoretically the same way as guardrails on roadways. On roadways, guard rails are installed alongside roads to keep a car from crashing into opposite lanes of traffic during an accident. When a train derails, train track guard rails are supposed to catch the train’s wheels, preventing it from completely running off the track or, like in this case, running into support structures.

Investigators point to a fracture pattern found in the section of rail that broke apart. While analysis of the rail found no signs of fatigue or flaws, they did find the break pattern consistent with overstress. Union Pacific officials acknowledged the disrepair as the cause behind the July 2020 derailment. “We determined that the cause was a wide gauge due to the ties and fasteners in that location at POD [point of derailment] being in disrepair,” Union Pacific officials said.

Not the first derailment

The NTSB report detailed what steps Union Pacific took to repair the damaged tracks after the first derailment. The report states the first incident, in June 2020, was caused by a “wide gauge” condition of the tracks. The report also noted that during bridge inspections dating back to 2016, the south end of Tempe’s Salt River bridge was missing the inner guardrail that is supposed to begin before the bridge and continue along the bridge structure’s tracks. The report shows that the bridge’s railroad ties were also undersized on either side.

Damage estimates from Union Pacific put the total repair cost at just over $11 million.