Studies show three lanes reduce crashes

    The Iowa Department of Transportation (DOT) presented crash statistics on three-lane roads at a Washington Street Committee meeting at the former library Wednesday. The DOT plans to repave West Madison Street in 2012, and when it does so it can repaint the lines from a four-lane to a three-lane configuration. The DOT wants to know by April which configuration the city council supports. The repaved portion would extend from Highway 1 to Second Avenue, which is just short of a mile. 

    A three-lane road is essentially a two-lane road with the middle lane reserved for left-turning traffic. DOT representative Troy Jerman showed evidence that reconfiguring a road from four to three lanes has reduced collisions every time the DOT has tried it, often reducing the number of crashes by 50 percent.

    Jerman said three-lane roads are much safer for turning traffic. He showed the audience a diagram of a four-lane road in which cars from opposite directions both wanted to turn left at an intersection. To turn safely, each car must be able to see the oncoming cars in the outside lane, but the oncoming left-turning car blocks their view of the outside lane.

    ?It?s amazing what a passenger car can hide,? said Jerman. ?If it?s in the right line of sight, it can hide a school bus.?

    Under a three-lane regime, the left-turning cars would be closer to the oncoming cars so they would have a better angle to spot them farther down the road.

    Jerman told the audience about a study the DOT did in the town of Sioux Center in northwest Iowa. The DOT did one of its first four- to three-lane conversions in that town in 1999. The DOT studied the flow of traffic and the number of crashes before and after the switch to three lanes.

    The study revealed that the three-lane road reduced average speeds in the city by 25 percent. The number of people who went more than five miles per hour over the speed limit dropped 75 percent. Crashes fell considerably from 30 to 10. Injuries went from 10 to zero.

    Street committee member Bob Shepherd commented that the intersection of highways 92 and 1 is dangerous. He said it is because cars from the south that want to turn left have to wait so long for a gap in the traffic. A line of cars forms behind them, and this makes them anxious to go. This makes them liable to take risks they ought not to take. Shepherd asked Jerman if a three-lane road would reduce that kind of risk.

    Jerman said three-lane roads are safer for the cars trying to enter them because the traffic on a three-lane goes slower than on a four-lane.

    ?You don?t have as many lanes to cross at a time when you enter a three-lane,? he said. ?If all the cars are in a line, it?s going to be a longer line and you think you wouldn?t be able to turn onto the street. But every time someone stops to turn, it slows everyone else down and creates that gap, which allows other cars to enter the street.?

For more, see our March 3 print edition.