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Study Shows Application of Diverging Diamond Interchange is More Robust Than First Thought

New Interchange Concept Could Save Country Billions of Dollars while Improving Traffic and Safety

A new interchange concept called the Diverging Diamond Interchange can be used in many more scenarios than previously thought according to Gilbert Chlewicki who is the leading expert nationally on this interchange design. The new finding is very significant in the transportation world because it will allow transportation departments to construct better interchanges at a considerably lower cost.

The Diverging Diamond Interchange (DDI) is a relatively new interchange concept that was introduced by Chlewicki in 2003. The design takes the form of a diamond interchange form with a twist. From the highway, the interchange looks like any other diamond interchange form, with one ramp off the highway and one ramp on to the highway. However on the cross road there is something quite different. As traffic approaches the first ramp, the intersection is adjusted so that traffic will be placed on the opposite side of the road. At the second set of ramps there is another crossover intersection that returns traffic back to the right side of the road.

By moving traffic to the left side of the road between the ramps, it allows left turns to be free flowing from the cross road. Because the left turns are now simplified, there is often no need for extra lanes that are built just for the left turning traffic. The design also simplifies the traffic signals by eliminating the need for left turn signals.

Previous studies indicated that the DDI should only be considered in locations with a high traffic volume of left turning traffic or if there was a strong directional movement during the peak hours.

This new study showed that the DDI can actually be applied in most situations when a diamond interchange form would be used with traffic signals. The study also showed that the DDI becomes a more effective interchange option versus other diamond interchange forms when there is more traffic in general.

The implication of this study shows that the DDI has a much greater chance of showing up in a community near you in the near future. Transportation departments are more likely to consider the DDI for many more of their interchange projects that allow traffic signals on the cross street.

Already the DDI is becoming a popular option in many transportation agencies due to its efficient design to move traffic safely with fewer delays at a lower costs. Some projects show that the DDI is estimated to be lower project costs by over 80%. One project in Indiana is estimating a project cost savings of nearly $60 million using the DDI. The main cost savings comes from the reduced amount of lanes needed above or below the bridge structure, which is almost always the most expensive part of any interchange project.

The first DDI in the United States opened to traffic in Springfield, Missouri in June 2009. Currently five DDIs exist in the United States, with dozens more being designed or constructed throughout the country.

Popular Science named the DDI one of the six best engineering innovations of the year in 2009. Articles on the DDI have also appeared in USA Today, Time Magazine, Roads and Bridges, and Engineering News Record. More information on the DDI can be seen at www.divergingdiamond.com.

Chlewicki has recently started a new transportation consulting firm based out of Maryland that specializes on the DDI and other innovative highway designs that improve traffic operations and safety at low costs. The firm, Advanced Transportation Solutions, aims to educate and assist transportation agencies on the benefits of these designs and how to optimally apply each design.