Instinct has nothing to do with engineering diagrams.
That’s the rub for engineers who have struck upon a potentially cheaper, safer and more efficient highway interchange design that would force Americans to drive on the “wrong” side of the road.
The Federal Highway Administration is proposing a three-year study of driver reaction to a new interchange design that could reduce traffic congestion and crashes involving drivers turning onto highway ramps from overpasses.
“This interchange is more cost effective and might function better under certain conditions than any design we currently have,” said Jim Daves, vice president of Parsons Brinckerhoff Inc., a Denver-based engineering firm.
The new design, dubbed the Double Crossover Diamond Interchange, would be used in areas where drivers turn left on an overpass to reach highway on ramps. The new design eliminates the need for drivers to cross oncoming traffic by shifting lanes on the overpass all the way to the left.
But that forces drivers from both directions to cross over for the length of the overpass onto what in the U.S. is considered the wrong side of the road.
The design can be cheaper than building large looping ramps — such as those in clover-shaped interchanges — that let drivers turn right onto an on ramp, Daves said. But, he said, the crossover design will fluster drivers trained to avoid driving on the left with oncoming traffic on their right.
“People are slow to change,” Daves said. “It’s got the negative that you are driving on the wrong side of the road, and that’s something that they don’t like to do.”
The Federal Highway Administration’s study would figure out if certain signs can show drivers what to do and if people get disoriented when oncoming traffic is on the right. Only one of the crossover interchanges is in service in the U.S. — completed in July in Springfield, Mo. The study would include simulators to see how people respond.
Signs are essential to introducing new intersections, said Alan Horowitz, University of Wisconsin-Milwaukee professor of civil engineering and director of the university’s Center for Urban Transportation Studies.
Problems associated with roundabouts show what happens when the signs don’t work, he said.
“Signing on roundabouts is really critical,” Horowitz said, “and we have not done a good job of it in the United States.”
It would be easier to use signs to direct drivers on the new crossover interchanges, Horowitz said. The circular design of a roundabout is difficult to translate into arrows on a sign, especially if there are two lanes in the circle, compared with the simpler crossover drivers perform on the new interchange, he said. Drivers also pick up confidence when they see others around them doing the same thing, he said.
Daves said his company proposed a crossover interchange last year for a project on a six-lane road in Pueblo, Colo. He said the proposal was rejected, but not necessarily because of the new design. He said he is open to trying it again.
“We will if we think it’s the right solution,” he said.
The ultimate test of the design will be to see how it works in the real world, Horowitz said.
“Eventually, you have to build it,” he said, “and you never know what’s going to happen until you build it.”