Illinois tollway planners hope diverging diamonds will be a motorist's best friend when innovative engineering tactics are applied to a reworked interchange at Elmhurst Road and the Jane Addams Tollway (I-90).
The atypical design, called a diverging diamond interchange, was first introduced in the United States in 2009 in Missouri.
Since then, a number have cropped up across the country. Illinois has none now, but three are in the works.
A diverging diamond interchange is intended to allow safer, smoother traffic flow on busy roads that intersect with highways. Essentially, it briefly shifts traffic into opposite lanes using signals on bridges or underpasses so that vehicles can turn left onto the highway without facing oncoming cars. Then, traffic is routed back to the right side of the road.
"Elmhurst Road and I-90 is an ideal location for this new and innovative design because the configuration requires drivers to temporarily cross over to the opposite side of the road -- eliminating potential conflicts between left-turning vehicles and vehicles traveling straight and allowing drivers to enter and exit the interchange more safely and efficiently," tollway spokeswoman Wendy Abrams said. "The diverging diamond design at Elmhurst Road will also use less land, reduce costs and maximize traffic flow on the ramps."
Work on the project starts later this year when the tollway will build a new road to take southbound Elmhurst Road traffic over I-90. The interchange will be completed in 2016.
"The design allows us to maintain traffic on the existing bridge while the other bridge to the east is being built -- minimizing the impact of construction on drivers," Abrams said in an email.
The Illinois Department of Transportation is working on two other diverging diamond interchange projects -- one at Route 59 and the Reagan Memorial Tollway (I-88) in Naperville and another on I-57 in downstate Marion.
Although the counterintuitive design sparked resistance at first -- with skeptics saying it would confuse drivers and cause accidents -- Missouri Department of Transportation officials, for one, say it works well and has increased safety.
Although the diverging diamond interchange is at I-90, it's actually part of the Elgin-O'Hare Expressway extension and western bypass of the airport the tollway is building. Tollway engineers at a Wednesday finance committee meeting estimated that up to $30 million to buy land for the project is needed so far.
In addition, the agency will spend about $316,250 to pay the Federal Aviation Administration to study how and if the extension and bypass will affect airport operations.
Tollway directors also authorized spending about $18.4 million to acquire land for widening I-90 between Rockford and O'Hare.