An entirely new kind of traffic interchange for southern Arizona will start to take shape. Local construction crews, along with the Arizona Department of Transportation, have been working on a project to improve access to Interstate 10 at Houghton Road.

The new $24.4 million interchange — an innovative design called a diverging diamond — will improve safety and traffic flow in a rapidly growing area of Pima County east of downtown Tucson.

The diverging diamond design has a major difference from the existing standard diamond interchange in place today: Traffic on Houghton Road will make a temporary shift to the left side of Houghton Road while crossing the freeway. This allows for left turns onto entrance ramps without waiting at an additional traffic signal. The design promotes safety because drivers turning left don't cross traffic while entering the on-ramp.

Traffic engineers chose this design because it can handle higher traffic volumes in the growing southeast Tucson area, where traffic is expected to increase by as much as 50 percent by 2045.

The new Houghton Road bridge will feature six lanes of traffic, compared with two lanes on the existing structure. Also, the project will improve access for pedestrians and bicyclists. ADOT has developed a construction plan that minimizes traffic impacts by building the new Houghton Road bridge while traffic continues to use the existing structure.

During the first week of construction, traffic impacts were minor as crews began clearing areas in the work zone and mobilized equipment.

The entrance ramp from Houghton Road to eastbound I-10 and the exit ramp from westbound I-10 to Houghton Road have closed, and will stay closed for nearly three months. The full closures of the two ramps will allow crews to reconstruct the ramps in one phase. Traffic will be detoured to the Colossal Cave/Wentworth Road interchange.

The project is scheduled for completion in late 2021.

More than 115 diverging diamond interchanges are in use in the U.S. as of mid-2020, including two half-diverging diamond interchanges on the Loop 202 South Mountain Freeway in Phoenix. A full diverging diamond interchange is scheduled to open at Interstate 17 and Happy Valley Road in Phoenix later this year.

For more information about the project and diverging diamond interchanges, please visit azdot.gov/i10Houghton.

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