Drivers will be using the state’s first major Diverging Diamond traffic interchange at Interstate 17 and Happy Valley Road this month, according to the Arizona Department of Transportation (ADOT).

The last stages of work are under way on the new, larger Happy Valley Road bridge over I-17 that provides much-needed additional traffic capacity at the interchange.

The Diverging Diamond design includes intersections on each end of the interchange that allow traffic to cross and use the left side of the Happy Valley Road bridge over I-17. That improves traffic flow by limiting traffic signal changes and allowing drivers to make direct left turns to enter freeway on-ramps without crossing in front of opposing traffic, according to ADOT. The design enhances safety by reducing conflict points for traffic.
Diverging diamond interchange design has grown in popularity across the country because of the traffic and safety benefits. The $50 million project also recently removed the roundabouts at the I-17 and Happy Valley interchange. They had been in use for the past two decades to help transition traffic across the older, narrower bridge at the limited freeway interchange. The roundabouts, installed as an interim measure, could be replaced once funding for the current project was made available. That happened through the Phoenix area’s Regional Transportation Plan approved by county voters in 2004.

ADOT also has reconstructed the interchange at Pinnacle Peak Road as an expanded traditional diamond interchange that features a wider bridge with more lanes in each direction. Crews also are finishing work on new lanes in both directions along I-17 between Pinnacle Peak and Happy Valley roads. Drivers can expect closures and lane restrictions at times until the project wraps up.