TUCSON, Ariz. — All lanes of the Houghton Road interchange at Interstate 10 are now open as the Arizona Department of Transportation (ADOT) has completed a new kind of interchange for southern Arizona.
The $24.4 million project features a diverging diamond interchange, which highway officials say will improve safety and traffic flow in a rapidly growing part of southeast Tucson.
Unlike a traditional diamond interchange, each direction of Houghton Road traffic temporarily shifts to the left while crossing the freeway. This allows for left turns onto the entrance ramps without waiting at an additional traffic signal. The design also promotes safety because drivers turning left don’t cross traffic while entering the on-ramp. Signals, signs and pavement markings help guide drivers through the interchange.
The interchange features larger entrance and exit ramps, along with more space for traffic to merge onto I-10 westbound. Over the freeway, the old two-lane Houghton Road bridge has been replaced with a structure that features six lanes and improved access for pedestrians and bicyclists.
ADOT traffic engineers said they chose the diverging diamond design because it can handle higher traffic volumes in the growing part of the southeast Tucson area, where traffic is expected to increase by as much as 50 percent by 2045.
ADOT minimized traffic disruption by keeping most of the interchange open during the project, which began in August 2019.
While all lanes are open, intermittent lane restrictions are possible in the next two weeks as construction crews wrap up minor project details. In the spring, drivers should expect overnight lane restrictions when warmer overnight temperatures allow for final paving on I-10 and the ramps.
More than 115 diverging diamond interchanges are in use in the U.S., including two half-diverging diamond interchanges on the Loop 202 South Mountain Freeway and a full diverging diamond interchange I-17 and Happy Valley Road in Phoenix.
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