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A traffic signal light flashes warning signs about approaching traffic at the HWY 37 and HWY 46 intersection in Bon Homme County. (Matt Gade / Republic)

At key intersection, rural alert system working well so far

TRIPP — So far, so good for an upgraded area intersection in Bon Homme County, where a pair of state highways meet.

The intersection of South Dakota Highways 37 and 46 was the first intersection in the state to receive a Rural Intersection Conflict Warning System, which alerts drivers of vehicles on the intersecting road of oncoming traffic.

Since its installation in August 2017, the intersection has had one right-angle crash and no fatal collisions. The South Dakota Department of Transportation is attempting to eliminate the right-angle crashes — also known as T-bone crashes — that are the most deadly.

South Dakota Department of Transportation Project Development Program Manager Mark Leiferman said the intersection — which is located about 10 miles south of Tripp and 15 miles east of Wagner — and its results are being closely watched.

"It's definitely a fit for where we have crashes occurring," Leiferman said. "You have drivers who might not be aware of a stop sign and that flashing beacon is there. It's not going all the time and it's making you aware of what's happening on the opposite leg of the intersection."

The system works similar to a regular traffic signal, with traffic detector loops identifying vehicles on the side road and sending that information to a flashing light on the primary highway. The goal is to prepare drivers for a vehicle at the intersection and potentially help reaction time if a stopped driver pulls out into the intersection.

The system is not blinking when vehicles aren't approaching. At the intersection, two large yellow lights blink and an electronic board lights up, saying "TRAFFIC APPROACHING."

Previously, the intersection had a blinking stop light for east-west drivers and a blinking yellow caution light for north-south drivers that were always on. Large stop signs remain in place for east-west drivers.

Previously, the intersection had experienced nine injury incidents and a fatal crash since 2006, according to the South Dakota Intersection Crash Diagram mapping function on the state DOT's website. About 1,100 vehicles travel through the intersection north-south on Highway 37 per day, while Highway 46 drivers going east-west number about 700 per day, according to the state's traffic count data.

The intersection did have a crash Aug. 1 in which a vehicle did not yield. That event resulted in non-serious injuries, according to the DOT database.

"We still need to monitor it and research it, but we've seen generally good things so far," Leiferman said.

The effectiveness in South Dakota can't yet be proven, Leiferman said, but the early signs have been good. In Minnesota, numerous systems have been installed in rural areas and post-installation studies in Minnesota indicated a 60 percent reduction in fatal or serious injury crashes.

"If there's something that can raise the awareness for drivers, and alert them, that's going to only be a good thing," he said.

The cost of the Bon Homme County system was about $150,000, funded completely through federal sources.

Another intersection conflict warning system was installed last month at the intersection of U.S. Highway 281 and South Dakota Highway 20 in Spink County near Mellette. Highway 281 is a divided highway there, and that is expected to provide the state DOT data about the success of the technology on four-lane roads.