I-10 collapse puts spotlight on Arizona bridge safety

Nearly 1,000 bridges in Arizona are labeled as problematic by the Federal Highway Administration.

There are 8,035 highway bridges in Arizona in the 2014 National Bridge Inventory Database, compiled by the federal government. Of those, 256 are considered structurally deficient and 684 are functionally obsolete.

That means almost 12 percent of Arizona’s bridges are labeled problematic by the feds.

Structurally deficient bridges have a significant defect, which often means speed or weight limits are needed to ensure safety, or that parts need to be monitored and repaired. Functionally obsolete bridges are considered either too small or poorly suited for modern-day traffic.

The Tex Wash Bridge along Interstate 10 that failed in California on Sunday had been deemed “functionally obsolete.” Inspectors believe that intense rains eroded the land around the Tex Wash bridge in California, causing one side of the eastbound span to collapse and forcing the closure of the westbound span.

Along I-10 alone in Arizona, there are at least 23 bridges considered structurally deficient and at least 98 bridges labeled functionally obsolete, like Tex Wash.

But being labeled as either functionally obsolete or structurally deficient does not mean the bridges are necessarily in danger of collapsing or unsafe to use, said Tim Tait, an Arizona Department of Transportation spokesman.

“If it was unsafe, it would be closed,” Tait said.

Even with 940 listed as problematic, Arizona’s bridges are highly rated nationally, Tait said.

“That still puts us with one of the top bridge inventories in the nation,” he said.

Several lists have Arizona in the top five states of least problematic bridges in the country.

ADOT spends $40 million annually on its bridge preservation program, Tait said, and bridges also are improved as part of roadway work. He said it would cost between $1 billion and $5 billion to fix all the structurally deficient bridges in Arizona.

There have not been any special inspections by ADOT since the California bridge collapse, Tait said.

ADOT crews in the Yuma area, which includes I-10, have been performing normal checks of roads, including bridges, Tait said, and have been inspecting bridges on I-8.

“We are actively inspecting bridges on I-8 as part of our regular inspection process,” Tait said.

Pingbo Tang, assistant professor in the Del E. Webb School of Construction at Arizona State University, said generally Arizona’s bridges are in good shape. “Arizona is a new state, and there aren’t any earthquakes,” Tang said.

The only issue Tang sees when inspecting bridges in Arizona is scouring, which is the washing away of soil near a bridge’s foundation. Tang said he recently inspected a bridge in Gilbert that had evidence of scouring. He said the bridge is safe, but erosion around the foundation is something inspectors have to watch out for.

Bridge ratings have not been terribly predictive of what bridges will fail when.

The Tex Wash Bridge’s eastbound portion, built in 1967, was given an A rating last year with a “sufficiency rating” of 91.5 out of 100, according to 2014 data. The bridge also had one of the highest possible flood-safety ratings, meaning it should have withstood even the heaviest rainfall.

In Washington State, the I-5 bridge that collapsed over the Skagit River in 2013 was not listed as structurally deficient, although it was considered functionally obsolete. The bridge had a sufficiency rating of 57.4 out of 100 before collapse.

The westbound I-35 bridge that collapsed over the Mississippi River in Minneapolis in 2007 was rated structurally deficient in the years before it collapsed, and it had sufficiency rating of 50 out of 100. A score of 50 generally means the bridge needs to be replaced.

More than 150 bridges in Arizona had sufficiency ratings of below 50 in 2014, according to federal data.