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Diverging diamond interchange opens at Interstate 17 and Happy Valley Road

Chloe Jones Arizona Republic (CNT) City News And Talk #phoenix-az

The Arizona Department of Transportation announced Sunday that the new diverging diamond interchange at Interstate 17 and Happy Valley Road opened for traffic on Sunday, replacing what had been roundabouts since 2001.

The diverging diamond design includes intersections and traffic signals that allow drivers to cross and travel on the left side of the new bridge over Interstate 17, ADOT said in a statement. Motorists make direct left turns onto the freeway on-ramps instead of waiting in front of oncoming traffic.

The interchange is opening in phases, and it is currently open in a temporary configuration while construction on the rest of the interchange is completed this fall. ADOT said there will be some lane restrictions on Happy Valley Road and Interstate 17 exit ramps until completion.

The intersection at Happy Valley Road and Interstate 17 is where a drunk driver entered the freeway going the wrong way and killed himself and two sisters in April 2017. People had long called the intersection confusing and called for changes to improve clarity and safety.

The project was pitched in July 2017, along with two interchanges on Loop 202 South Mountain Freeway, which opened in December 2019. The diverging diamond design is said to enhance traffic flow while improving safety at busy interchanges.

ADOT said the reconstructed interchange reduces conflict points for traffic, allows more lanes on the Happy Valley Road bridge, improves on- and off- ramps and has fewer traffic signal sequences.

This comes as part of a $50 million project that began in November 2018 to reconstruct the Interstate 17 interchanges at Happy Valley Road and Pinnacle Peak Road, ADOT said. Interstate 17 has also been widened in both directions between Happy Valley and Pinnacle Peak roads. It’s funded in part by Maricopa Association of Government’s Proposition 400, a dedicated sales tax for transportation approved by Maricopa County voters in 2004.

The interchanges on Loop 202 are considered “half diverging diamonds” because “the cross streets intersecting with the freeway do not extend south of the interchange,” said ADOT spokesperson Doug Nintzel. Adding that ADOT recently broke ground on another diverging diamond interchange at Interstate 10 and Houghton Road in Tucson. 

ADOT said crews also reconstructed the I-17 interchange at Pinnacle Peak Road, one mile south of Happy Valley Road. It is being reconstructed as a traditional diamond interchange with more lanes and turn bays on the bridge over Interstate 17. This interchange is also expected to be completed later this fall.