One of the most innovative interchange concepts to come along in the past few years is the diverging diamond interchange (DDI). It is also called a "double crossover diamond" interchange by FHWA. The concept originated in France. There are currently 2 open to traffic in Missouri, one under construction in both Tennessee and Utah.
A DDI design requires traffic to crisscross over to the left side of the roadway, separated by concrete barriers, between the proposed traffic signals located at the interchange ramps. This design eliminates several conflicting vehicle movements, particularly the left turns onto the ramps to US 129 Bypass, without the need for costly reconstruction of the existing bridge to provide the additional lanes that would be normally be necessary for other interchange designs.
Example DDI in Missouri
The Missouri Department of Transportation just opened a second DDI on July 12, 2010 and has received favorable public comments including the following:
"MoDOT gets a lot of complaints, but I wanted to say WELL DONE on the overpass project which officially opened on Monday, July 12th. The work the contractor(s) did by maintaining traffic flow had to be difficult at best, considering the amount of traffic in that area, but, the "traffic jams" were minimal at best. I go through that intersection 5-6 times at day, and welcome the new design, especially in the evenings, when the left turn lane always backs up. I was one of those that was against the new idea when it was first installed at I-44 & Kansas Expressway, but have become a convert and think ALL interchanges should be diverging diamonds. They are extremely efficient at cutting down on left turn crashes, and move a higher volume of traffic, in a shorter period. Again, thanks to MoDot and the contractors for a JOB WELL DONE!"
DDI under construction in Alcoa, TN. Designed by Gresham Smith and Partners
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