Not quite used to roundabouts yet? Just wait for diverging diamond interchanges

Posted at 5:00 AM, Dec 19, 2018
and last updated 2019-01-11 17:43:59-05

COLUMBUS, Ohio — By now, you're familiar with all the roundabouts popping up around the Tri-State.

Transportation experts say the little loops, which turn two- and four-way stops into circles with yield signs, increase safety. Federal Highway Administration data indicate severe traffic crashes were reduced by 82 percent at intersections that had once been two-way stops when they were replaced with roundabouts.

Now, another set of new-fangled traffic configurations are making its way to our area.

They're called diverging diamond interchanges or double crossover diamonds, and construction is set to begin on three in the Tri-State in 2019.

"(The interchange) simplifies the amount of movements that have to be made and therefore increases the volume that can be put through an intersection," Butler County Engineer's Office deputy Dale Schwieterman said.

The first such interchange in the area will be constructed in West Chester at I-75 and Union Center Boulevard. Although the name might sound intimidating, he promised navigating the interchanges will be easier than it sounds.

"The concept will be pretty easy for the drivers," Schwieterman said. "It will be fairly intuitive when they come up to it."

Here's how it works:

Drivers start out traditionally on the right side of the road and transition to the left side of the road. Those making left turns can turn left without oncoming traffic, and those continuing straight will cross back to the right side of the road.

The Kentucky Transportation Cabinet plans to build two of the interchanges in Boone County at I-71/75: One at the Mt. Zion Road exit and one at its Richwood Road counterpart.

"The problems in traffic is making left-hand turns, so you're always turning in front of oncoming traffic," KYTC spokesperson Nancy Wood said. "This is eliminating that."

The first diverging diamond interchange in Ohio opened in 2013 at I-270 and Roberts Road in the Columbus area. According to Ohio Department of Transportation spokesperson Breanna Badanes, left turn and angle crashes were nearly eliminated in the two-year period after the interchange opened.

There were 11 left turn crashes at the Columbus area-interchange in 2012. By 2015, there were none. Angle crashes were also reduced between 2012 and 2015 from seven to one.

"Angle crashes tend to be the most severe types of crashes, so reducing angle crashes is a significant safety improvement," Badanes said.

Meghan McCurdy drives through the Columbus-area interchange daily, and she likes it now that she's gotten used to it.

"I think in the beginning it was a little bit of a challenge to understand the flow," McCurdy said. "But once I did and I think everyone else around me, we just kind of figured it out."

Meanwhile, the interchange has also seen an increase in traffic since it opened. The average daily traffic was nearly 38,000 vehicles per day in 2013, according to ODOT. The current average is over 46,000 vehicles.

"Our two big things we really look at are capacity and safety," Schwieterman said.

He said the Union Center Boulevard interchange averages 45,000 vehicles a day; that's at least twice the amount of traffic projected when the Union Center exit opened 20 years ago. There is still land available around the interchange; if developed, it could bring additional traffic in the future.

"This will help us serve the future traffic as well as the existing traffic," Schwieterman said.

West Chester will use tax increment financing, or TIFs, to pay for improving the intersection. The cost projection is $13 million. Meanwhile, KYTC was able to secure a federal INFRA grant worth $67 million to cover the cost of the two interchanges planned in Boone County. Despite costs in the millions of dollars, the interchanges are considered a lower cost option than traditional interchanges.

Construction in West Chester and Boone County is expected to begin in the spring of 2019.

WCPO 9 On Your Side is introducing a year-long series of reports in 2019 called "Move Up Cincinnati" dealing with the topics of transportation and growth in the Cincinnati region. We have a team of reporters contributing to this project on air and online. We will examine where, when and how the region is growing and the impact that growth is having on the Tri-State.