By Starrla Cray
McLEOD, CARVER COUNTIES, MN From traffic volume to accident counts, not all of Highway 7’s crossroads are created equal.
“There are four main types of intersections two-way stops, all-way stops, signal lights, and roundabouts,” said Minnesota Department of Transportation (MnDOT) engineer Paul Kachelmyer. “Each one of these has pluses and minuses to it.”
Kachelmyer was the project engineer for two roundabouts along Highway 7 that were installed midway through 2008. One is at Carver County Road 10, and the other is at Highway 25, north of Mayer.
For those two intersections, roundabouts were deemed the best traffic control choice to reduce accidents.
“What was happening there were bad right angle crashes,” Kachelmyer said. “Cars going across Highway 7 would pull out in front of cars going 60 miles per hour.”
According to national statistics, there is a 90 percent reduction of serious injury accidents after a roundabout is installed, and a 60 to 70 percent reduction in overall accidents.
“Roundabouts are terrific at reducing right-angle crashes,” Kachelmyer said.
Near New Prague, for example, an intersection had 50 injury crashes and two fatalities over a five-year period. Three years after a roundabout was installed, there were four minor accidents.
“The reduction was dramatic,” Kachelmyer said.
After a roundabout is installed, it often takes a while for accident counts to decline, because drivers are getting accustomed to the new intersection, according to Kachelmyer.
In 2009 and 2010, a total of 9 accidents occurred at the intersection of County Road 10, according to MnDOT data. Six of them were classified as “property damage only.”
From 2001 to 2008, a total of 43 accidents occurred at that intersection, including 22 “property damage only” crashes.
At the Highway 25 roundabout, 10 crashes occurred in 2009 and 2010, seven of which were “property damage only.”
From 2001 to 2008, the total number of accidents was 56, including 30 recorded as “property damage only.”
McLeod County Road 9 and 1 are both two-way stops.
Since 2001, 26 accidents have been reported at the County Road 9 intersection, and 30 at County Road 1.
According to MnDOT assistant traffic engineer Mike Lownsbury, MnDOT does not currently have plans to change traffic control at those two intersections.
“Our district covers 12 counties, so with all of the demand for our funding, it gets spread pretty thin,” Lownsbury said.
McLeod County is in District 8, which covers Chippewa, Kandiyohi, Lac qui Parle, Lincoln, Lyon, Meeker, Murray, Pipestone, Redwood, Renville, and Yellow Medicine counties.
“They have ratings for every road, and intersections in the state are ranked from worst to best,” Lownsbury said.
“We look at what the circumstances are, and what potential solution might help,” Kachelmyer added.
Traffic volume data is calculated every few years, according to Lownsbury.
“We put out mechanical traffic counters at different locations, and leave them there for 24 to 48 hours,” he said.
About 3,300 vehicles are on Carver County Road 25 near Highway 7 per day, according to MnDOT data. On Highway 7, between 7,800 to 8,800 vehicles travel near that intersection daily.
The traffic increases to the east, with 3,850 to 4,500 vehicles intersecting at Carver County Road 10, and 8,800 to 10,200 along Highway 7 per day.
Farther from the Twin Cities, traffic tends to decrease.
Along McLeod County Road 9, there are 930 to 1,600 vehicles passing through each day, with about 6,900 on Highway 7 near that intersection.
Traffic picks up slightly at the intersection of McLeod County Road 1, which goes from Winsted to Lester Prairie. Daily, about 2,700 to 4,400 vehicles travel along McLeod County Road 1, and 6,800 vehicles travel in that area on Highway 7.
When an intersection is especially congested, traffic lights are often utilized.
“A lot of people don’t know that the purpose of a traffic light is to regulate traffic flow,” Kachelmyer said. “Most people would think it’s safer, but accident rates usually go up when signal lights are put in.”
However, severe accidents are often reduced, he added.
One example is on Highway 36 near Stillwater, where a traffic light was installed seven years ago. After the light was added, accidents were up by 70 percent, but the number of people seriously injured was cut in half.
“The traffic volume was way too high to make a roundabout reasonable,” Kachelmyer said.
The criteria for installing a roundabout or traffic light is not narrowly defined.
“It’s very much a case-by-case basis,” Kachelmyer said. “It’s a judgment call.”