ADOT proposes diverging diamond interchange to replace roundabouts

Phoenix — The Arizona Department of Transportation (ADOT) is proposing a diverging diamond interchange to replace roundabouts at the Interstate 17/Happy Valley Road interchange as a way to provide efficient and safe traffic flow for a growing area of north Phoenix.

A diverging diamond interchange has one major difference from standard diamond interchanges common around Arizona: Local street traffic makes a temporary shift to the left side while crossing the freeway, allowing for direct left turns onto entrance ramps without waiting at an additional traffic signal.

In examining options, ADOT determined that a diverging diamond interchange would be better able to manage the growing volume of traffic at Happy Valley Road and reduce the amount of time drivers spend waiting at traffic signals. It also enhances safety by reducing the number of points where directions of travel conflict.

More than 80 diverging diamond interchanges have been constructed in 29 states since 2009.

ADOT’s I-17 project also will include reconstructing the I-17 interchange at Pinnacle Peak Road, still as a traditional diamond interchange but with increased traffic capacity.

ADOT continuously seeks innovative approaches to enhance safety and improve traffic flow, and the diverging diamond configuration is one of the tools available as interchanges are built or upgraded. Diverging diamond interchanges also will be built at two locations along the Loop 202 South Mountain Freeway: Desert Foothills Parkway and 17th Avenue.

The updated Regional Transportation Plan managed by the Maricopa Association of Governments, the regional transportation planning agency, provides funding for a project to reconstruct the I-17 interchanges at Happy Valley and Pinnacle Peak roads, scheduled to start as soon as fall 2018.

ADOT designs and constructs Phoenix-area freeway improvement projects based on the 20-year Regional Transportation Plan approved by Maricopa County voters in 2004.