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Study of two-lane highways offers insights into head-on collisions

by Michael Kirk - March 27, 2006

In 2003, head-on collisions on American roads accounted for 10 percent of traffic deaths, a recent study shows.

UConn researchers looked at road conditions related to the occurrence of these accidents and their severity, and what Connecticut can do to help prevent them.

The study was funded by the New England University Transportation Center, a program sponsored by the U.S. Department of Transportation.

The researchers, led by John Ivan, an associate professor of civil and environmental engineering, studied 720 different 1-kilometer segments of two-lane highways in Connecticut and the head-on collisions that occurred on them over a five-year period.

Ivan worked with University of Maine professor Per Garder, and the study examined roadways in that state as well. Nationwide, 75 percent of traffic fatalities occur on two-lane roads.

“With the population here in New England continuing to spread outside urban areas, traffic volumes are increasing on two-lane rural roads, and we can expect the frequency of head-on crashes to increase,” Ivan says.

Nationally, 83 percent of two-lane undivided road crashes occur on rural roads, and the possibility of a fatality in a head-on crash is three times higher in rural areas.

Ivan and his team first looked at how road design correlated with head-on collisions. Not surprisingly, areas where head- on collisions are most likely to occur are:

  • roads with frequent curves that require more steering to navigate;
  • roads with sharp turns;
  • and roads that rise and fall, temporarily blocking a driver’s view of oncoming traffic.

The study showed that the severity of head-on collisions increases when:

  • the road surface is wet;
  • the paved surface is less than 30 feet wide;
  • there are a lot of business and retail driveways along the road;
  • and between 10 p.m. and 6 a.m.

The study notes that the density of access points on the road – driveways for businesses or retail areas – and where they are located are related to the outcomes of head-on crashes.

Specifically, having a large number of office driveways is correlated with less severe crashes, while having a large number of retail-use driveways is associated with more severe crashes.

This suggests that people may drive at higher speeds in retail areas, or that the traffic in their vicinity is higher at night, when the most severe crashes occur, Ivan says.

The results of a head-on collision.
Photo supplied by John Ivan

“Obviously, head-on collisions occur when drivers cross the center line, and many of these accidents happen because it is late at night and they are drowsy and accidentally cross the line, or because they lost control of the car,” he says.

“So more signs and pavement markings are not going to address the problem. What will help reduce these kinds of crashes is keeping drivers alert or preventing such crossings of the center line.”

This can be done by installing ‘rumble strips’ in the center of the road and creating a raised median at the center on curves. The state department of transportation has tried this on Route 6 in Bolton, he says, but residents complained about the noise caused by vehicles’ driving over the rumble strips, so they were paved over.

Since retail areas appear to experience more severe crashes, and perhaps have fewer residents to complain, it may be most beneficial to install such treatments in those areas.

Ivan says some of the report’s findings also apply to roads with more than two lanes.

“While Route 44 on Avon Mountain is a multi-lane rather than a two-lane road, some of these lessons can be applied there as well,” he says.

“The proportion of head-on crashes there is similar to that on two-lane roads, and remedies that would prevent such crashes on two-lane roads would work on a multi-lane road as well.

Certainly, widening the pavement beyond a total of 50 feet will only encourage drivers to go faster than the limit for negotiating some of the sharper curves.”

Two of the road segments examined are parts of Route 44 in Coventry.

“While the best way to address the problem is to reduce or straighten the number of moderate to sharp curves on roadways, trying to design straight, flat rural roads in a place like New England would be prohibitively expensive,” Ivan says.

“Adding a six-foot shoulder on the side of the road can reduce the severity of these crashes, because it gives drivers additional space to maneuver. Ivan notes, however, that often when roads are widened, 8- to 10-foot shoulders are added.

“This study indicates that anything greater than six feet carries no additional safety benefits,” he says. “In fact, roads that are too wide encourage greater speed by drivers, making them less safe.”

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