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Diverging diamonds might save lives on Chicagoland roadways

Two new examples of a new type of interchange, or meeting to two major roadways, are now under construction in the Chicago area. Drivers are often confused and concerned when they first hear about the interchange idea, invented only in 2000 for a student term paper. Still, the design has quickly caught on among urban planners and highway engineers.

Advocates say the “diverging diamond interchange” (DDI) has gotten mostly good reviews where the design has gone into service. It’s said to reduce traffic accidents significantly in addition to being less expensive to build and leaving a smaller footprint on the land.

What is a DDI?

DDIs are hard to explain in words and diagrams or even in videos and simulations. Many drivers report understanding them only after having used one and, even then, some drivers say they don’t even notice they’ve passed through a DDI.

The main goal of a DDI is dealing with the problem of exiting or entering a major highway by making a left turn into the path of oncoming traffic. Instead, the DDI first (and briefly) switches the traffic to the British plan, where traffic going the opposite direction is on your right, and then allows you to make your left turn.

Data on Chicago’s DDIs is accumulating

Drivers, state and local governments, and infrastructure designers and construction firms all share potential liability for deaths, injuries, pain and suffering and other damages caused by their negligence. It’s one of many reasons they keep a close eye on road design and its effect on crash statistics.

The world’s first DDI was built in Springfield, Missouri, in 2009, and there are now roughly 130 either built or in the works.

Four years ago, Naperville received one at the interchange of I-88 and Rouge 59, and Des Plaines saw another more than two years ago at I-90 and Elmhurst Road. They joined the state’s first such interchange, in Marion, near the southern tip of the state.

Because the design is new, especially in the Chicago area, the real-world safety statistics are still being collected. With time and each DDIs, the data becomes more statistically significant by the day. The DDI concept is said to reduce the number of crashes between vehicles, whether minor fender-benders or major injury/fatality incidents. The statistics on the toll DDIs take on pedestrians is more difficult to assess, at least from media reports.

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