ADOT's $6 million project to replace the 50-year-old deck on the El Toro Road bridge is underway and work isn't coming to an end any time soon.
The Arizona Department of Transportation is trying to pull off the multi-phase project with as little disruption as possible, especially difficult in an area where there are few alternative routes for Interstate 19 drivers.
But Rod Lane, ADOT's Southcentral District engineer, said the project will roll out while still maintaining the level of traffic on the interstate. That means no lane closures — and that's the tricky part.
"If traffic volumes are low, it's easy because then you can just reduce the width and you wouldn't have any backups," he said. "But in the case of I-19, you have very high traffic volumes. So if we try to drop a lane in each direction to try and reduce that width we're going to have huge backups and it's not going to work."
Anyone here when Vice President Mike Pence came to Green Valley in October knows how bad traffic can get after I-19 closed and Nogales Highway was the best alternative. Or what happens when a crash closes one or all four lanes.
So how do you replace the entire deck of a bridge without closing a lane? Work in stages, shift the flow of traffic, and create a bit more space for everybody.
In El Toro Road's case, there are two separate bridges spanning the road, which is between Duval Mine and Sahuarita roads. Each has two lanes going north and south. ADOT had to look at the separate spans and consider how much surface area was available to reduce the width of the lanes while still maintaining two lanes in each direction safely.
"We couldn't get two lanes in each direction on one bridge, it was impossible," Lane said.
ADOT's first phase involves making the southbound bridge wider. That's where they are now.
The current work, by the way, has nothing to do with possible ADOT connections for two new proposed interstates — the Sonoran Corridor (which would link I-19 and I-10) and Interstate 11, a parallel freeway that isn't scheduled to be built for decades.
The new, wider section of bridge under construction now will make the deck replacement possible without having to reduce the lanes in either direction.
Under the bridge, ADOT has El Toro Road closed while crews strip the edge of the southbound bridge and add a new column and abutment.
About 10 to 12 feet of the existing bridge needs to be removed where ADOT will put the additional section of the bridge and new deck.
Once ADOT completes building a whole new section of bridge from the ground up on the southbound side, they will shift traffic from the northbound lanes to the new southbound deck. That will also mean building a crossover road.
ADOT will then strip and replace the deck of the northbound bridge and add upgraded side barriers – removing the steel tubes for a solid concrete style. Lane said the concrete barriers are a safety improvement over the current tubed barriers.
Unlike the southbound bridge, the northbound will only have the decking and barriers as structural changes; everything else will remain the same.
With the northbound bridge complete, traffic headed toward Tucson will return to its regular route while southbound traffic gets shifted to the extended portion of the other bridge. Then the final phase of replacing the remaining old deck on the far west side can be completed.
Lane expects the entire project to be completed in the fall.
Planning for it
Replacing the entire deck of a busy bridge doesn't come without challenges.
While the different phases address the logistics of keeping traffic flowing, there are also engineering challenges to make sure it remains safe for travel during the process.
"The challenge is figuring out where you're actually going to cut the deck relative to the beams and finding out if you have enough room," Lane said. "It's really a geometric problem. Geometric-slash-structural engineering problem."
Knowing where to cut to ensure the bridge remains stable is what engineers at ADOT keep their eyes on when undertaking these projects, he said. However, with the right planning, the bridges should still be able to handle the same traffic volume during the work.
"There'll be no impact," Lane said. "We may have to slow the speed limit down a little bit from time to time, but other than that we should be good."
Any work that might impede traffic would likely take place at night to avoid rush hour, he added.
"Number one, it's out of the traffic times," he said. "Number two, it's better conditions for concrete. Concrete likes kind of cool air. It works better to do it at night."
Adding to the complications is the railroad line running under the bridge. Lane said that while this rail line is less active than other projects, such as Ina Road in Tucson, it still takes some coordination and corrugated steel to keep the trains moving.