ONLY ON KOLD: Broken Bridges? - Tucson News Now

ONLY ON KOLD: Broken Bridges?

Although some Bridges in Pima County receive low inspection grades, vehicles are still allowed to cross them. (Source: Tucson News Now) Although some Bridges in Pima County receive low inspection grades, vehicles are still allowed to cross them. (Source: Tucson News Now)
TUCSON, AZ (Tucson News Now) -

Drivers in southern Arizona cross highway bridges thousands of times a day without a second thought.

Yet, many of the bridges are in dire need of repair.

Bridges in Pima County go through regular inspections - and although some receive low inspection grades, vehicles are still allowed to cross them.

A bridge collapse at the I-10 Tex Wash Bridge in Desert Center, CA, brought the issue into fresh scrutiny in July after heavy flooding weakened the bridge's foundation.

Despite the bridge's "A" grade under Federal Highway Administration standards, the bridge itself still failed.

"What happened in California could happen anywhere in the world," Arizona Department of Transportation spokesman Doug Nintzel said.

Nintzel said even though a bridge is deemed structurally sound, there could be times when Mother Nature is stronger.

"If you have record rainfall that comes down, and you have events with runoff that (are) record-setting, you could have a problem with the bridge," Nintzel said.

Transportation departments rely heavily on a "sufficiency" rating system that shows which bridges need the most attention after a weather event or from regular wear-and-tear. Of the 4,841 state highway bridges in Arizona, less than two percent, or approximately 100 bridges, are listed as "structurally deficient," according to the latest data provided by ADOT.

It may sound dangerous, but ADOT officials said the definition can be misleading.

"It does mean we've identified repair needs that we are going to address, but it does not mean a bridge is close to falling down or that you shouldn't drive on it," Nintzel said.

Nintzel said what happened at the Tex Wash Bridge should not be indicative of the state of Arizona's highway bridges, and that Arizona's bridges hold up well in comparison with bridges across the U.S.

Dr. Mo Ehsani, professor emeritus of civil engineering at the University of Arizona, acknowledged this, saying Arizona's bridges are relatively young - about 30 to 40 years old - compared with bridges in other states.

Ehsani said Arizona's bridges are for the most part built with a combination of beams and concrete slabs - a system that is far stronger than the trussing system that older bridges use.

Arizona's drier weather is also a benefit.

"We have a good climate that helps a lot in making them more durable," Ehsani said.

Despite the favorable conditions, many bridges in southern Arizona are still in need of retrofitting and repairs. With heavy rain expected this El Niño winter, several bridges will be watched closely.

"Our antennas go up. When we hear about El Niño, there's no doubt that we're going to want to pay attention to what's going on," Nintzel said.

Ehsani and Nintzel said Arizona's bridges are uniquely at risk during seasonal flooding. "Scour vulnerability" is a term used to determine which bridges are most vulnerable after a weather event like a monsoon storm.

"You have such a high velocity of water running, through the riverbeds, this washes out a lot of the soil around the foundation," Ehsani said.

ADOT said it tracks these conditions under its scour retrofit program that monitors which bridges need reinforcements after a storm. Weather notwithstanding, some bridges in southern Arizona have also deteriorated from everyday use.

The westbound I-10 overpass over Ina Road, for example, has visible cracks and gaps along its concrete deck.

Due to its condition and the frequency in which it is used, ADOT has given it a high priority among the list of bridges that are up next for repairs. ADOT is replacing the bridge as part of a major modernization project next year.

"Mostly because we want traffic to be flowing better at the interchange. We want to switch it to taking Ina Road over I-10 as well as over the railroad tracks because that will help so much more in moving the traffic in the area," Nintzel said.

But bridging the gap between the need to fix and the limited funding to do it is also a constant struggle - particularly at the local level.

"The biggest thing is competing against other type of roadway projects," said Pima County Department of Transportation Engineering Division Manager Rick Ellis.

Ellis said the county puts weight restrictions on problematic bridges until money is available to fix them. In Pima County, 14 bridges currently have load limitations.

"We're trying to prolong the life span of it. So I haven't maybe stopped the deterioration, but I'm going to stop the effect of deterioration," Ellis said.

One of the bridges with weight restrictions, the Union Pacific Railroad bridge at Houghton Road has a sufficiency rating of 11 percent, according to recent data provided by Pima County DOT.

Due to its low rating, the bridge will be replaced as part of a greater widening project that is being led by the city of Tucson, Ellis said.

Another load limit was proposed for the Elephant Head bridge over the Santa Cruz River near Green Valley, but has since been lifted because repairs are now scheduled.

Even though more than a dozen of Pima County's bridges received low sufficiency ratings, the county wants to reassure the public they are safe to cross.

"None of our bridges are at risk. That's the biggest thing we want to reinforce to the public, and we use that in every opportunity that we can," Ellis said.

But Ehsani said so-called "Band-Aid" fixes like load limits, may not be enough to fix the problem in the long run.

"Putting a load rating on a bridge, yes, it does help in terms of potentially saving lives, but that's not the longer term plan. These bridges are supposed to be able to carry the full load of the traffic," Ehsani said.

As for how frequently state and county bridges are inspected, Pima County DOT conducts bridge inspections every two years. In-depth inspections of the county's steel bridges and fracture-critical bridges are scheduled every four years.

Bridges with weight limitations are inspected every 12 months and those with scour vulnerability are inspected post-flooding, according to Pima County DOT.

Of Arizona's 4,841 highway bridges, 2,271 are "traditional" bridges that are inspected every two years. 2,570 qualify as culverts, which are inspected every four years.

Related link

Southern AZ bridges with some of the lowest ratings

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