How Elmhurst Road diverging diamond should work

Illinois tollway planners predict drivers and pedestrians - guided by traffic signals - will find navigating the Elmhurst Road and Jane Addams Tollway (I-90) interchange safer once a somewhat counterintuitive redesign is constructed.

The "diverging diamond" interchange will be complete in 2016 at the same time ramps providing access to and from the west and other improvements are finished.

It works by briefly shifting traffic into opposite lanes using signals on bridges or underpasses so that vehicles can turn left onto the tollway without facing oncoming cars.

Then, traffic is routed back to the right side of the road. The design uses less space than traditional cloverleaf interchanges and is cheaper to build.

Movement should be more efficient because of free-flow turns, engineers contend.

A 10-foot wide, shared-use, enclosed path for pedestrians and cyclists will be built in the median of the interchange.

People on foot or with bikes will cross at traffic signals using designated crosswalks.

"With pedestrian access down the middle, there will be less conflicts with traffic," senior project manager Hope Garrett said at a tollway open house.

The Illinois Department of Transportation is building another diverging diamond interchange at I-88 and Route 59, set for completion in fall 2015.

The Missouri Department of Transportation introduced diverging diamond interchanges to the United States in 2009 and has built three. They have been used in France.

Although the Elmhurst Road diverging diamond interchange is at I-90, it's actually related to the Elgin-O'Hare Expressway extension and western bypass of O'Hare International Airport that the tollway is building.

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