By Daria Kadovik
Rush hour. Long delays. Too many cars. Nowhere to go.
Phoenix might get its first divergent diamond interchange to replace the Happy Valley roundabouts.
At a packed public meeting July 25, the Arizona Department of Transportation made its case for the divergent diamond interchange on Happy Valley Road and Interstate 17 intersection.
Many residents of the surrounding neighborhoods know the struggle. It could take 20-30 minutes during rush hour, to pass through the intersection.
“It gets backed up pretty early, around 3 p.m., and it stays backed up till 6 p.m.,” said Jordan Lemos, a 24-year-old resident of the area. “There is really no way to avoid it, because Pinnacle Peak gets backed up too.”
ADOT presented the diverging diamond interchange where, according to ADOT website, 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.
The DDI comes with many benefits, including processing higher volumes of traffic, reducing the number and severity of collisions, reducing wrong-way movements, and reducing the number of conflict points.
The interchange might look confusing, but “it is very obvious where to go,” said Scott Johnson, a consulting traffic engineer from HDR Engineering Inc. for the DDI project.
The Federal Highway Administration study showed that DDI helps reduce overall collisions by 50 percent and reduce fatal collisions by 60 percent unlike any other intersection. However, the reduction of wrong-way drivers is more prominent to Phoenix.
According to the state Department of Public Safety, 740 wrong-way drivers have been reported on Arizona freeways since the beginning of 2017.
“DDI aims to eliminate wrong-way drivers with the prevention system,” Johnson said. “It makes it almost impossible to make the wrong-way movement. They would have to physically want to and try to make this right turn.”
The new interchange will also accommodate bicyclists and pedestrians. Current interchange provides no safe passage for these two groups. With the new interchange, cyclists get to stay on the right side of the road in a bike lane, when pedestrians get multiple crossing to get to the other side of the freeway, according to Johnson.
The new interchange will also support the future expansion of the Interstate17 to five lanes plus an HOV lane, according to Al Shah, a project manager for the DDI. The construction plan is to remove existing roundabouts and add more lanes to have three lanes in each direction.
“We analyzed traffic operations all the way out to the 2035 design year and added another 20 percent traffic projection volume on top of that, and the DDI still works,” Johnson said. “DDI is not a short-term improvement, it’s a long-term improvement.”
The DDI was first constructed in Springfield, Missouri, in 2009. Today there are more than 90 DDIs throughout United States that perform well, Johnson said. It seems like a viable solution to handle high volumes of traffic and use taxpayers’ money in the best way possible.
ADOT also covered the traffic changes that will be made to the Pinnacle Peak intersection. Pinnacle Peak is a traditional diamond interchange with a narrow bridge span. It does not accommodate future I-17 expansion, as well as, pedestrians and bicyclists, according to ADOT.
The new expansion will include two through and two left turn lanes in each direction, that will accommodate future freeway expansion, pedestrians, and bicyclists, according to Shah.
“Sometimes you have to wait two or three lights to cross 23rd Avenue,” Lemos said. “It does not support all the traffic flow during rush hour.”
The DDI and Pinnacle Peak expansion project will cost about $49.5 million of taxpayers’ money. The construction is set to begin in fall 2018, according to Shah.