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Civil Engineering Magazine THE MAGAZINE OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS

MnDOT Addresses Deadly Intersections

By Kevin Wilcox

An innovative roadway configuration has dramatically reduced serious crashes on divided highways in rural areas.

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Some RCI designs include a reinforced shoulder to accommodate U-turns by large trucks. Minnesota Department of Transportation

April 4, 2017—In rural area across the United States, there is a type of intersection that traffic safety engineers and emergency responders know all too well. These at-grade intersections involve a small local road that crosses a divided multilane highway, and they are the sites of many right-angle, high-speed crashes. When emergency responders are called to one of these intersections, they know to brace themselves for fatalities and serious injuries.

In recent years, several departments of transportation across the country have attempted to solve this problem with a configuration variously referred to as a restricted crossing U-turn, a JTurn, or a reduced conflict intersection (RCI). In this type of intersection, motorists on the local road intersecting the highway who wish to cross the highway and continue or turn left on it must instead make a right turn at the intersection. They must then move into a left-turn lane a short distance down the highway and make a U-turn at a designated location. They can then proceed along the highway or turn right and thus continue on the local road. For motorists on the divided highway, the traffic pattern is unchanged. They still have left-turn lanes enabling them to turn left on the local road if they so desire.

The Minnesota Department of Transportation (MnDOT), which has built 12 of these intersections in the past seven years, recently completed a safety study examining their performance. The results are stunning. Fatal and serious right-angle crashes were eliminated entirely, and crashes that resulted in injuries were reduced 50 percent.

"Our experience so far from our perspective has been great," says Derek Leuer, P.E., a principal engineer at the MnDOT. "We've had a 100 percent reduction [in fatalities]. It doesn't get much better than that."

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In an RCI, all traffic from the minor road must make a right turn onto the divided highway. Motorists who want to continue on the minor road then make a U-turn from a designated lane, and a right turn back onto the local road. Spack Consulting

Leuer notes that there are several theories as to why these at-grade crossings are so dangerous to begin with. He believes that, upon reaching the highway, motorists on the local road have difficulty judging and mentally processing the closing distances of vehicles approaching from both the left and the right. And motorists on divided highways in sparsely populated rural areas tend to speed.

"When you are sitting at an intersection perpendicular to the [highway] trying to gauge a vehicle going 70 to 75 miles an hour, your brain is just not wired to process that correctly," Leuer says.

An RCI isn't the only solution to the problem. A grade-separated intersection with a bridge across the divided highway also is effective. But those overpasses typically cost $7 million to $20 million to construct and often carry a low volume of traffic, sometimes just 500 vehicles per day. That compares with an average cost of $750,000 for an RCI to accommodate the same number of vehicles.

Another option that certain states, Minnesota among them, have tried is placing traffic signals at the intersections. And while that approach has sharply reduced right-angle crashes, in Minnesota it has dramatically increased the overall number of crashes in that speeding motorists struggle to stop for an unexpected red light on an otherwise open highway.

Given the combination of dramatic safety improvements and reasonable cost, why aren't RCIs more common? Initial public opposition is the reason, Leuer explains. When MnDOT engineers present this approach at public meetings, they are often given this advice: "Brace yourself."

As Leuer puts it, "Anytime we have proposed these, we get remarkably stiff public opposition. Our engineers who've gone out to these meetings … will tell you they are some of the ugliest public meetings they have ever done."

He attributes this in part to how counterintuitive the traffic pattern appears when people are first exposed to it. Leuer notes that even some seasoned engineers are skeptical of the RCI until they see the safety results.

"It is extraordinarily counterintuitive to tell somebody [that], to go right, make a U-turn and then come back is safer than just crossing the road. To most drivers, that just doesn't make any sense," Leuer says. However, the percentage of crashes that involve U-turns in Minnesota is very small, and RCIs make U-turns safer by providing dedicated lanes from which to make them. "There is a general perception [that] U-turns are risky maneuvers," Leuer says. "So I think when people make U-turns, they usually do them with a great deal of caution."

Public resistance can extend to the local trucking and emergency responder communities, which can see RCIs as a hindrance. The MnDOT has studied truck traffic on an RCI at Cologne, in the southwestern part of the state. The tight highway alignment there meant that the RCI had to include reinforced shoulders to provide extra room for trucks. But even with that, trucking companies planned to avoid the intersection and use an overpass about a mile away.

"We were under the impression that trucks don't use it," Leuer says. "But we went out there, and it was unbelievable the number of trucks that we saw. We were out there for five days, and we actually counted 400 heavy trucks going through it."

Leuer advises other transportation agencies that want to consider RCIs for their rural at-grade intersections to expect public opposition and to counter that with detailed presentations explaining why the alternatives won't work as well or don't fit into the budget. Also, holding preliminary meetings to win over key local stakeholders can make the process much smoother.

The MnDOT plans to deploy 21 new RCIs over the next five years and is beginning to consider them systematically, on a corridor-level basis, rather than on a case-by-case basis. "At the end of the day, it's hard to argue with a 100 percent reduction of your target crash type," Leuer says.

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