Diverging Diamond Interchange

The LaCrosse Street Diverging Diamond Interchange (DDI) in Rapid City and the 41st Street DDI in Sioux Falls were designed to enhance safety and address future travel needs in high volume intersections within two communities experiencing population growth. The DDI design improves safety by reducing vehicle conflict points.

LaCrosse Street was the first DDI within the State of South Dakota with construction completed two years ago. Dustin Witt, Highway Safety Engineer, provided crash data comparisons for the five years leading up to construction and the two years since DDI completion. Dustin noted, “The Lacrosse Street interchange was averaging over 18 crashes per year prior to construction. With just over two full years since opening, crashes have reduced to less than 7.5 per year.”

This indicates a reduction in crashes of over 58%, while simultaneously improving the operations of the interchange.

The 41st Street project, located at Interstate 29 in Sioux Falls, was the first DDI on the eastern half of the State. It has been operational for nearly one year. Dustin states that the 41st Street interchange was averaging over 100 crashes each year prior to construction. As we near the one-year mark of opening, the DDI is on pace for less than 30 crashes which is more than a 73% reduction in crashes. 

This crash reduction is even more significant during the first year, which in theory, includes potential driver uncertainty about navigating a DDI intersection.

Data as of June 1, 2025