Bringing natural forms onto roads and bridges was the idea behind the artwork on the new Happy Valley Road bridge over Interstate 17.

By now, many motorists have likely noticed the purple slashes and blue diamonds on a white background that adorn the new overpass wall. Metal pipes form gentle swells along the wall, adding to abstractions that, put together, form the shape and color of natural mountains.

“Blue diamonds are like stars merging with the landform silhouettes,” said Joe Salazar,  aesthetic designer/coordinator for aesthetic landscaping and designs for ADOT.

On the concrete just below the wall is a line of brown diamonds, representing the thorns of the Sonoran Desert saguaro. This abstraction is taken a step further with the vertical patterns on the sides of the bridge. These represent the ribbing of the saguaro, he said.

“It is unfolding the trunk of the saguaro, laying it out and putting the pattern over the wall,” Salazar said, “It is a continuation of the saguaro.”

And that's the pattern you are seeing in the lower photo to the right.

 

The new overpass that bears this design is an integral part of a safety- and traffic-flow improvement project encompassing I-17 interchanges at Happy Valley and Pinnacle Peak roads in north Phoenix.

The project also included the new diverging diamond intersection at Happy Valley. In addition to reconstructing the traffic interchanges, ADOT and the Federal Highway Administration have added a travel lane on I-17 and replaced a box culvert on Pinnacle Peak Road to the east of I-17.

For Salazar, who was joined in the project by Phoenix artist Daniel Mayer, the artwork on the new intersection reflects the surrounding natural environment.

“If you drive along I-17 and look at your surroundings you will see what is remaining of the natural desert,” he said. “I was trying to bring that in.”

For more information about this joint Arizona Department of Transportation and Federal Highway Administration project, visit the project's page on our website.

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Art of Transportation
We think there is beauty in transportation. It’s not all hard hats and pavement. Art of Transportation is a blog series featuring unique photos our team has taken while on the road or on a construction project.

As part of ADOT’s recent major project along Interstate 17 in north Phoenix, the reconstruction of the bridge and traffic interchange at Pinnacle Peak Road often took a backseat to the rebuilding also taking place at the busier, nearby interchange at Happy Valley Road.

After all, the I-17/Happy Valley Road interchange received more attention because it was reconstructed as a diverging diamond with new – and different for Arizona – lane configurations and traffic signal setups. 

But enough about Happy Valley Road. We’re here to sing the praises of the new and improved Pinnacle Peak interchange. What a difference a couple of years and hard work can make.

As you can see in the video to the right, the Pinnacle Peak Road interchange now features a much wider bridge crossing over I-17. The old, more narrow bridge was demolished as part of the $50 million project that delivered the upgraded interchanges at Pinnacle Peak and....that other interchange a mile to the north.

Before this project, traffic on Pinnacle Peak Road often backed up approaching I-17, especially in the westbound direction during rush hour. Drivers had to wait in fewer lanes for traffic signals to change.

Now, there are left turn bays with two lanes for traffic entering I-17. That means more “storage capacity” for traffic making those left turns. The I-17 on- and off-ramps at the Pinnacle Peak interchange also were reconstructed with more lanes that provide drivers with improved options at the interchange. The traffic signals are all new and the interchange is much more aesthetically pleasing with individual red paver blocks used to fill the raised median islands.

The modernized, larger Pinnacle Peak Road interchange along I-17 is now in place to efficiently handle today’s traffic as well as traffic in the area for decades to come. We just want to let the new bridge and other improvements at Pinnacle Peak get a little time in the spotlight.

The reconstruction project was funded in part by Proposition 400, a dedicated sales tax approved by Maricopa County voters in 2004.

It’s happening!

The new diverging diamond interchange (DDI) at Interstate 17 and Happy Valley Road is scheduled to open to motorists sometime in mid-October.

The innovative Arizona Department of Transportation interchange paves the way for a slew of benefits: Better traffic flow, fewer “conflict points” between traffic traveling in opposite directions and thus, improved safety.

ADOT has worked closely with the city of Phoenix and Maricopa Association of Governments (the Valley’s freeway planning agency) in designing and now building the state’s first major diverging diamond interchange. The DDI design has been growing in use across the country for its innovative features. 

As mentioned above, diverging diamonds provide safety benefits by reducing the number of conflict points at intersections within the interchange. Those are locations with opposing directions of traffic. A potential conflict exists every time a vehicle crosses or turns across the path of another direction of traffic.

For example, at the Happy Valley Road DDI, intersections and traffic signals will allow drivers to cross to the left side of the bridge over I-17 and thus have a direct turn onto the freeway on-ramp. They are able to make that left turn without facing traffic in the opposite direction.

Reducing such conflict points as well as overall traffic-signal movements also allows more traffic to move through the interchange in a shorter amount of time. That helps to limit wait times for drivers, especially during times of busier traffic.

While you may be unfamiliar with such an interchange, studies and observations in other states have shown motorists quickly get the hang of traveling in a DDI. The use of noticeable pavement markings also helps direct traffic. You can see how it all works in the video to the right..  

ADOT State Engineer Dallas Hammitt discussed the benefits of a DDI in a blog earlier this year about two smaller diverging diamonds (called “half DDIs”) now in use along the Loop 202 South Mountain Freeway.

“This type of interchange works by temporarily transitioning traffic to the left side of the road, allowing through-traffic and left-turning traffic to proceed through the interchange simultaneously, eliminating the need for a signalized left turn.”

Crash rates improved dramatically after a diverging diamond interchange was constructed in Springfield, Missouri, according to the Federal Highway Administration. The study compared crashes from the first year after construction to the five-year average before, and found the following:

• Left-turn crashes were totally eliminated.
• Right-angle crashes were reduced 72 percent.
• Rear-end crashes were reduced 29 percent.
• Total crashes were reduced 46 percent.

“Where they have been built,” the FHWA report said, “travelers save time, agencies saved money, and communities will benefit from safer facilities for many years.”

It was going to happen sooner or later. And it was later than some drivers would have wanted. But here in August we’ve bid farewell to the two roundabouts on separate ends of the Happy Valley Road bridge that traveled over Interstate 17 in north Phoenix.

In fact, we also said goodbye in recent months to the old Happy Valley bridge that used to connect to those circular roundabouts. The demolition of the old bridge and removal of the roundabouts have now taken place as part of the construction of a much larger, much more modern bridge and diverging diamond interchange at I-17 and Happy Valley Road.

While the old Happy Valley roundabouts operated for some two decades and certainly were criticized by many a local driver over time, there is another side of the story. In their defense, the roundabouts did what they were designed to do. 

In the late 90s, there just wasn’t funding available to pay for a larger and wider bridge to carry Happy Valley Road over the freeway. In order to make the I-17 interchange still work with local projects that were widening Happy Valley Road as it approached the freeway, ADOT researched alternatives and studied the use of roundabouts in other parts of the country.

The Happy Valley roundabouts allowed for the need for traffic on a wider Happy Valley Road to transition down onto the existing and narrower two-lane bridge over the freeway. That would have been much more difficult, if not impossible, to do with traffic signal intersections. 

The roundabouts were always designed as an interim measure until such time when enough regional funding was available to construct a new freeway interchange. That happened as part of the Regional Transportation Plan for the Phoenix area that was approved by county voters in 2004. The plan allowed for the $50 million project that is now scheduled for completion this fall.

Crews have been building the new diverging diamond at I-17 and Happy Valley Road as well as a more traditional diamond interchange at Pinnacle Peak Road. We’ll have more about the diverging diamond in an upcoming blog.

Although the time and funding had come to replace the Happy Valley roundabouts, there are plenty of examples where roundabouts will continue to safely move traffic. That includes highway intersections in the Verde Valley and beyond. If you’re using them, please remember to follow the rules of the roundabout, including slowing down as you approach and yielding to traffic already in the circle.