Diverging Diamond Interchange

Diverging Diamond Interchanges (DDI) are a novelty here in the United States.  With only five in the country at the time of this post, the DDI design accommodates left-turn movements at signalized, grade-separated interchanges while eliminating the need for left-turn phasing.  Traffic crosses over to the left side of the roadway between the ramps of the interchange. The benefit is safety as the DDI design reduces the number of potential conflict areas.  In addition to the safety benefits, the design also offers significant operational and cost benefits over other design alternatives.

The most recent functional DDI Interchange in the United States was installed in Alcoa, Tennessee, and uses GridSmart to collect traffic data.  “We are excited to be among the first in the nation to utilize this innovative design solution which will improve mobility in Alcoa,” commented Andrew Sonner, P.E., city engineer, City of Alcoa, TN.”

See a video of how the DDI design works here.


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  1. Robert March 29, 2011 at 7:30 am

    There are currently 5 ddi’s in the US (3 in Missouri, 1 in Utah, 1 in Tennesee) and New York State just let a contract to build one this year in Rochester. Numerous others are in planning and design.

  2. WebMaster March 29, 2011 at 7:56 am

    Thanks to Robert for the clarification. I’ve updated my post to reflect this correction. It looks like DDI is proving itself to be a good solution! Thanks again for the comment!!

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