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This three-mile stretch of I-10 is Arizona's most 'dangerous' for crashes

Data from the Arizona Department of Transportation says the area of the SR-51/Loop 202 "Mini Stack" is among the busiest stretches of Valley freeways.

PHOENIX — A three-mile stretch near the heart of downtown Phoenix is among one of the most dangerous stretches of road for drivers in the Valley, according to data from the Arizona Department of Transportation.

The stretch near the downtown "mini-stack" where the I-10 intersects with SR-51 and Loop 202 saw more than 1,700 crashes in 2021. 

That same three-mile stretch also had the most crashes in 2020.

In an email to 12News, ADOT said:

"I-10 in the area of the SR 51/Loop 202 "Mini-Stack" interchange is among the busiest stretches of Valley freeways. Traffic volume and merging heighten opportunities for drivers to be involved in crashes."

"Stacks" are when multiple freeways are layered on top of each other. The idea is to provide an efficient system to get drivers to major highways.

However, the more roads and ramps there are the more potential issues.

“There’s lots of merging, diverging, a lot of weaving sections where people are weaving in and out of traffic,” Ram Pendyala, an ASU professor specializing in transportation engineering said.

“These types of stacks and interchanges just tend to be a very efficient way to make traffic flow," Pendyala said, "but indeed, there may be a tradeoff when it comes to safety.”

The mini stack on the I-10 could require drivers to cross multiple lanes of a busy highway to continue on one of the three roads.

“I don’t think it’s that surprising. The question is, what type of changes can we make?” Pendyala said.

The Maricopa Association of Governments is studying exactly that.

Projects on the "mini-stack" are challenging.

"Some of this is trying to figure out, within these big constraints that we have, what possible solutions are there. Really the solutions will be looking at address those conflict points are some of those weak points and really where the freeways come together," John Bullen, Transportation Economic and Finance Program Manager at MAG, said.

Bullen says that the mini-stacks are seeing more issues because Phoenix grew differently than originally projected. The designers believed the I-10 would carry most of the workload. 

However, the Valley has seen rapid growth along Loop 202, forcing more people to make the multi-lane change that can be dangerous.

Bullen says because of the location, they will not be able to tear down the stack but need to come up with other solutions. This Spring, they believed they had a way to fund any potential project.

“We have a significant amount of money allocated, more than $250 million, just to improve the mini stack itself,” Bullen said.

The problem is that $250 million was supposed to come from continuing a half percent sales tax by extending Prop 400. Legislation to put the proposal to the voters was vetoed by Governor Doug Ducey.

“Unfortunately, without the half-cent tax, we won't be able to do these big infrastructure projects,” Bullen said.

Both experts agree that if nothing gets done, the three-mile stretch will stay one of the most dangerous for years to come.

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