Are diverging diamonds safer than traditional intersections?

Diverging diamond interchanges (DDI) reduce crashes and improve traffic flow compared to traditional intersections.

There are three diverging diamond interchanges in South Dakota. The busiest two – Lacrosse Street in Rapid City and 41st Street in Sioux Falls – saw crashes fall in the year after they became operational.

Crashes were reduced by 58% in Rapid City and 73% in Sioux Falls in the months after the diverging diamonds opened.

The Sioux Falls interchange averaged more than 100 crashes a year before construction. As of June, it was on pace to have 30 crashes in its first year.

Diverging diamonds send vehicles to the left side of the road, allowing exits onto the interstate without left-hand turns across traffic.  Traditional intersections have about 25 conflict points that can lead to crashes. Diverging diamonds have 14. 

The first DDI opened in Missouri in 2009, and crashes fell 50%.