SIOUX FALLS, S.D. (KELO) — Drivers in Rapid City and Sioux Falls will be seeing something new as they cross over the interstates in the next two years. Each city will be getting a new type of intersection called a diverging diamond.
The diverging diamond appears to have been invented in the early 1970s in France. The Missouri Department of Transportation built the first one in the U.S. at a busy interchange in Springfield in 2009.
South Dakota’s first diverging Diamond will be built on the Lacrosse Street Bridge over I-90 in Rapid City. Drivers should see work beginning this month and intermittent on ramp closures.
“They are going to start doing some night they have to do some removal of the bridges over the interstate lanes so we will do some night closures here for a few nights and once that’s done you will start seeing more work in getting that new bridge in place to have in operations by this fall,” said Craig Smith the Operations Director for the South Dakota Department of Transportation.
The second Diverging Diamond will be placed on the 41st Street bridge over I-29 near the Empire Mall. Engineer, Harry Johnston is overseeing the two-year project that will include the widening of 41st Street from the interstate to Marion Road.
“It will begin here in March, the end of March we will begin construction on the west side of I-29, work on form Marion Road to I-29, and then from there, the interchange is scheduled to be worked on in 2023,” said Johnston.
A diverging diamond looks intimidating because you actually drive on the other side of the road, into the lanes we would consider oncoming traffic. But studies show they are easy to navigate, they move more traffic and they reduce the number of crashes by 37-percent.
“It’s going to be really difficult to drive that wrong, there are not a lot of decisions to make. You follow the lanes it will take you to the signal if you stop at the red the light turns green you proceed to the left side and it will take you right back to the right side once you get through that interchange,” said Craig Smith.
One of the main safety benefits comes from the left turn. Because you drive on the left side of the road, there is no oncoming traffic for those turning left, you simply get in the left-hand lane and drive onto the interstate.
“Give it a chance, pay attention when you drive through these new interchanges but I think in the end everyone is going to see it as a real positive and a benefit to those who drive that road every day,” said Smith.
The South Dakota DOT looked at diverging diamonds in other states before deciding to go ahead with Rapid City and Sioux Falls projects. The Assistant Chief Engineer for the Missouri Department of Transportation tells us they’ve learned a lot since installing the country’s first diverging diamond. He told me drivers will notice shorter cycle times, in other words, you won’t have to wait so long for that green light.
The South Dakota DOT and the City of Sioux Falls are so confident in the new design that two more are planned for Sioux Falls. One at I-229 and Benson road and the other at the Brandon exit on I-90.
The Department of Transportation and the city of Sioux Falls are hosting pre construction open house will this Thursday from 4 to 7 at the Empire Mall. There will be examples of how to navigate the Diverging Diamonds and people to answer questions.