There’s a great need for updated and increased infrastructure throughout the country. And Arizona is no different than other states in its quest to continually keep up with the expanding needs of its drivers. The Interstate 17 interchange reconstruction project at Happy Valley Road and Pinnacle Peak Road in north Phoenix is a prime example.

The north Phoenix area has seen a growth in population as well as traffic volume since 2000. I-17 now carries well over 100,000 vehicles per day near Pinnacle Peak Road. To compensate and meet the driving public’s needs, the $50 million I-17 project is overhauling two traffic interchanges spaced a mile from each other while also adding an additional travel lane in each direction along what is known as the Black Canyon Freeway.

Timing of the Project

Improvements at the two interchanges – Happy Valley Road and Pinnacle Peak Road – are long overdue according to Doug Nintzel, Arizona Department of Transportation (ADOT) Spokesman. “The existing roundabouts on each end of the soon-to-be-replaced Happy Valley Road bridge over I-17 were only intended as an interim intersection measure two decades ago.”

Although the project was a long time coming, the need to increase and improve infrastructure in the area has been clear to ADOT for some time. "We recognize that this north Phoenix stretch of I-17 serves as a gateway between the metro area and the communities of northern Arizona, including Flagstaff and Prescott,” said Nintzel. “ADOT has made major strides with improvements here over the past 15 years, including expanding the interstate from a four-lane rural highway to a modern, eight-lane urban freeway.”

Why now? The money finally became available. Nintzel notes, “Fortunately, there was funding in the Phoenix region's transportation plan to pay for the project.” The project is part of the Maricopa Association of Governments' Regional Transportation Plan (for the greater Phoenix area) approved by Maricopa County voters in 2004. Projects in the region are funded via a county-wide half-cent sales tax as well as the area's share of federal highway funds to establish a schedule and pay for freeway projects like the I-17 interchange project.

Multiple Elements

The project includes three main elements according to Julio Alvarado, ADOT's Resident Engineer on the project. “The prime contractor, FNF Construction, is reconstructing these two adjacent I-17 interchanges at Pinnacle Peak Road as well as Happy Valley Road. Before we’re done, crews also will have improved freeway capacity for years to come by providing the extra I-17 travel lanes in both directions north of Pinnacle Peak to the Happy Valley interchange.”

For drivers on Happy Valley Road, ADOT is constructing a new overpass over the freeway. The reconstruction will provide three through lanes in each direction, dedicated left-turn lanes, dedicated right-turn lanes, as well as bicycle lanes and pedestrian walkways. Other work includes construction of two exit lanes from northbound I-17 to Happy Valley Road. And the new overpass will accommodate possible future freeway widening below.

ADOT is removing existing roundabouts at Happy Valley Road and is constructing a Diverging Diamond Interchange (DDI) in its stead. Nintzel says of the decision, "We've been very interested in the expanded use of diverging diamonds around the country and impressed with how they have been shown to improve traffic movement with fewer traffic signal movements as well fewer conflict points for drivers. Improved safety and the ability to move traffic, especially during rush hours, were the primary reasons our design team recommended Happy Valley Road as a location that would benefit with a DDI."

Meanwhile, at Pinnacle Peak Road, crews are building a new tight diamond traffic interchange. "Pinnacle Peak Road doesn't experience as much traffic demand, so designers decided the old diamond interchange should be expanded with more ramp capacity and a wider bridge with additional turn bays and through lanes,” says Nintzel. “It'll be night and day when it comes to the larger interchange handling traffic along Pinnacle Peak Road."

Site Challenges

The north Phoenix area where the work is taking place has grown substantially in terms of housing and business development. I-17 is flanked by a large shopping mall, major employers, hotels, and nearby neighborhoods.

Working in a buy area along an already busy freeway presents challenges. "It’s been a challenge to accomplish the necessary work in this area,” says Alvarado. There are schedule restrictions in order to limit impacts on local traffic. “It's never easy meshing construction with daily traffic needs."

Construction on the I-17 project began in November 2018 and is expected to be completed on time in fall 2020. “We are on track to complete the project on time because so far we’ve accomplished key milestones such as girder installation and bridge deck construction at night and on weekends," says Alvarado.

One way to happily marry construction and daily traffic needs is to ensure motorists are clear on how the work will impact them. ADOT staff and partners have strived to keep drivers up to date. “Our communications team has worked closely with the City of Phoenix in keeping local residents notified with project updates via email, social media and a community relations hotline," says Nintzel. “Of course, it also helps to display planned restrictions on freeway message signs in the area.”

Upon completion, ADOT’s I-17 interchange reconstruction will meet two key goals: improved safety and expanded traffic capacity to serve both freeway and local drivers for decades to come. Updated infrastructure is just what the area and the country need.