Looking for a solution to reduce conflicts between vehicles at rural intersections, the South Dakota DOT implemented a Rural Intersection Conflict Warning System in 2017. The system is based on warning technology used by the Minnesota DOT to reduce right-angle crashes and reduce traffic injuries and fatalities.[i] South Dakota’s warning system project has been implemented in two locations: the junction of Highways 46 and 37 in Bon Homme County in southeastern South Dakota and at the intersection of U.S. Highway 281 and SD 20 near Mellette in Spink County.[ii]
The warning system consists of vehicle detector loops on the side roads of these rural intersections. The loop detection triggers a flashing light and electronic board sign with a message indicating that traffic is approaching on the side road. The lights and sign remain off when there is no side-road traffic approaching the main highway. The specific messaging triggered by traffic on SD 20 is “Traffic Entering When Flashing” and the traffic sign on U.S. 281 reads “Traffic Approaching When Flashing.”[iii]
The first conflict warning system in South Dakota is located where two rural two-lane highways intersect. This intersection has a long history of crashes. Between 2006 and 2017, the intersection of SD 46 and SD 37 had experienced nine injury crashes and one fatal crash. Different safety techniques have been deployed over the years to address the issue. A South Dakota DOT engineer had heard about Minnesota DOT installing warning systems and decided to try a similar pilot. South Dakota DOT hired Minnesota-based SRF Consulting to do the design, using concepts and advice from both Minnesota and Iowa projects. In the end, South Dakota wanted a system that was based on those concepts but was tailored to work for South Dakota’s conditions.
Minnesota DOT recently completed an analysis of the intersection conflict warning system installations in their state and have found that there have not been clear crash reductions in the past three to five years, although minor reductions indicate the potential for reduction of right-angle crashes.[iv] A separate usability study conducted by the University of Minnesota suggests that drivers might behave differently depending on the warning system’s design, including wording on the sign and how to use electronic components to indicate the sign is on and when traffic is approaching.[v] Both Minnesota and South Dakota DOTs plan to continue to evaluate its existing locations before installing the system at additional intersections. South Dakota also plans to monitor its pilot locations before adding more intersections. There has been one crash at the SD 46 and SD 37 intersection since 2017’s warning system installation. There is not enough data available at this point to draw conclusions about effectiveness of either of South Dakota’s warning projects.[vi]
The cost of the warning system infrastructure at the SD 46 and 37 intersection was approximately $170,000 including design. The second intersection at U.S. 281 and SD 20, where a divided four-lane highway intersects with a two-lane highway, cost $214,000 including design. Design includes detection type, loop or video sensors, and determining the amount of delay between the time a vehicle is detected and the light is triggered. Design also includes setting up the type of sign messaging.
In terms of maintenance, South Dakota DOT staff state that the intersection conflict warning system is similar to maintaining a traffic signal but on a smaller scale. Maintenance includes repairing damaged loops, restoring lost power, and maintenance specific to the technology. Maintenance is conducted by South Dakota DOT.
Public outreach about the intersection projects included
news releases shared through South Dakota News, media articles, and the South
Dakota DOT has posted video of the intersection warning systems on the South
Dakota DOT YouTube channel.[vii]
[ii] Traxler, Marcus (2018). At key intersection, rural alert system working well so far. Agweek, https://www.agweek.com/news/traffic-and-construction/4492524-key-intersection-rural-alert-system-working-well-so-far
[iv] Maranatha Hayes and Derek Leuer. Minnesota DOT (2019). A Study of the Rural Intersection Conflict Warning System, https://www.dot.state.mn.us/trafficeng/safety/docs/ricws-report.pdf
[v] Disi Tian, Nichole Morris, and David Libby (2018). Rural Intersection Conflict Warning System Evaluation
and Design Investigation, Center for Transportation Studies, University of Minnesota, https://conservancy.umn.edu/handle/11299/198534
[vi] Personal communication with Andy Vandel, September 2019
This report was delivered to the U.S. Department of Transportation in 2020. It was primarily authored by NADO Program Manager Rachel Beyerle and NADO Associate Director Carrie Kissel. Many transportation agency staff and others assisted with this project in a variety of ways. We offer deep and heartfelt thanks to all the individuals who have provided information and images, consented to be interviewed, and offered editorial guidance in support of this research. This work is supported by the U.S. Department of Transportation under requisition number HOIT190194PR. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of U.S. DOT or the NADO Research Foundation.