In search of 'Dead Man's Curve': Minn.'s DOT uses data to find dangerous roads
BRAINERD, Minn. — It's an oft-repeated anecdote: people always seem ready to offer an opinion of the most dangerous curves or intersections.
A study examining every mile of county roadways in the state seeks to identify those areas most at risk for crashes causing serious injury or death using science—before they happen.
Howard Preston, an engineer contracted to work with the Minnesota Department of Transportation, told the Crow Wing County Board Tuesday qualifying for federal dollars for safety improvements means proving some kind of crash problem. Based on those measures, nowhere in the state showed a big enough problem, Preston said.
"I've spent years looking for 'Dead Man's Curve,'" Preston said. "I can't find it. It doesn't exist in this state."
Preston said at the worst, engineers identified curves with two or maybe three crashes within a five-year period. But with 6,500 severe crashes over five years on the county highway and road system alone, there was room for improvement—and new science was applied to find the most effective ways to make those improvements. By comparing those areas overrepresented amid the crash data, common characteristics began to emerge.
"So we searched the system for characteristics, rather than crashes," Preston said.
Those risk factors were identified for road segments, curves and intersections—everything ranging from the traffic volume to the sharpness of a curve to the distance between stop signs. Those areas found to have three or more risky characteristics are considered higher priority for safety improvements.
Crash statistics bear out these classifications, MnDOT reported. Segments with five risk factors have eight times the crash density as those with zero risk factors. Factors associated with the greatest crash risk on rural county roads—above all other studied—were a distance greater than 5 miles to the last stop sign and commercial development at a rural intersection.
The goal, Preston said, is to assist county engineers with prioritizing fixes to get the biggest bang from the state and federal buck. In 2014, for instance, Crow Wing County used some of the data to install chevron signs on every curve on the county highway system. Installation of those signs is correlated with a reduction by more than half of off-the-road crashes, County Engineer Tim Bray said, and is a much less expensive solution than reconstructing a curve.
Preston said reconstruction of a curve could cost $250,000, while putting up chevron signs might run $1,000 with the federal government picking up $900 of that tab.
Some other solutions that might come about from identifying areas with the highest number of risk factors include where to place a roundabout or reduced-conflict intersection, where to smooth out the slope of a ditch or the most effective places to pave shoulders.
All of these are collected into "The Big Book of Ideas," an update to the County Roadway Safety Plan prepared for each of the state's 87 counties about five years ago. Minnesota was the first state in the country to analyze the roadways in each of its counties, Preston said.
From 2012-14, about $60 million distributed from MnDOT to county governments for road safety improvements was correlated with a 25 percent reduction in the fatality rate on county road systems.
Roundabouts and U-turns
Reducing crashes is as simple as installing a roundabout or a reduced-conflict intersection, also known as a restricted crossing U-turn. Although that's not quite as simple as it sounds, Preston said.
Roundabouts are responsible for reducing 60-90 percent of all right-angle crashes, those typically causing the most severe repercussions—but typically run a price tag of $1 million per intersection.
Reduced-conflict intersections, one of which was recently installed along the newly reconstructed Highway 371, reduce 100 percent of angle crashes, according to MnDOT's data, but run about $750,000 per intersection. These intersections are still a much cheaper price tag than a full-blown interchange, which can run between $10 million and $30 million.
All of these are preferred to traffic signals, however. Preston said signals are no longer considered safety features and are not supported by federal safety funds. Signals, along with complementary turn lane development, cost between $250,000 and $500,000.
"It's not cheap," Preston said. "It's not really a safety device."
Reduced-conflict intersections are a more cost-effective way to handle safety concerns associated with an intersection of an expressway, such as Highway 371, and a more rural county road, Preston said.
"Expressways are at risk, and what do you do?" Preston said. "You can't put traffic signals in. They don't work. This (reduced-conflict intersections) is a strategy that can be done, and is being done more and more across the state."
Prevention or reaction?
The discussion Tuesday turned toward County Road 115, also known as Ojibwa Road. The scenic road between Round and North Long lakes has long been the subject of controversy for the county highway department. While the pavement is nearing or past the end of its life in many spots along the road, some residents argue the road would lose much of its special character when undergoing reconstruction. Bray said crash statistics—the lack of crashes on the windy, narrow road—are used to support the argument of a simple overlay, versus a larger-scale construction project.
"His (Preston's) point of taking the analytical approach, rather than wait for people to literally stack up dead, as the reason to do a safety project, is the right approach," Bray said.
Preston said some of those same people might be those who, in a different scenario, might ask the county how many people have to die before they do something.
"At some point, something is going to happen, and now we have the science to get out in front of these things and be proactive," Preston said.