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The Dorsett diverging diamond interchange looking east. |
Dorsett Road and the Diverging Diamond Interchange Project History
The interchange was converted to a DDI in October 2010, and the project will be complete by the spring of 2011. Work on the sidewalks, landscaping and other enhancements continues. Construction began in the spring of 2010 on the diverging diamond interchange at Dorsett Road and Interstate 270.
Dorsett Diverging Diamond Fact Sheet (2 pages, 160 kb)
What were the problems with the existing I-270 and Dorsett interchange?
The Interstate 270 and Dorsett interchange was congested due to heavy traffic utilizing the interchange.
Why the proposed solution?
After presenting two alternatives at the public meeting, MoDOT proposed constructing the interchange as a diverging diamond interchange (DDI). Some of the advantages of a diverging diamond interchange include free turns for motorists, meaning vehicles don’t cross opposing traffic. Traffic models indicate this type of interchange works well with areas of heavy traffic, such as Dorsett Road.
The city of Maryland Heights will also be relocating Old Dorsett Road and Progress Parkway while this project is under construction. To visit the city of Maryland Heights Progress Parkway project website, click here
The diverging diamond interchange is a new type of traffic solution, meeting the needs of intersection safety, increasing capacity and decreasing congestion. The U.S. Department of Transportation Federal Highway Administration has more information about diverging diamond interchanges at the web site below.
http://www.tfhrc.gov/safety/pubs/07048/index.htm
The Missouri Department of Transportation has built three DDI's. The first diverging diamond interchange opened in the summer of 2009 at Interstate 44 and Route 13 in Springfield. It was the first DDI built in the United States.
Since then, a second diverging diamond interchange has also opened in Springfield. The interchange of Interstate 435 and Front Street in Kansas City was the first DDI approved by MoDOT, but won't be built for several years.
A cost savings
One of the benefits of building a diverging diamond interchange (DDI) at Dorsett is cost. Building a DDI at Dorsett saves taxpayers an estimated $13 million over the other option, a Single Point Urban Interchange (SPUI). A DDI needs less bridge structure than a SPUI. MoDOT will not have to lower Dorsett Road.
How much will the I-270 and Dorsett construction cost?
The Dorsett project is expected to cost $10 million. Other contributors include the city of Maryland Heights, St. Louis County and federal funds. MoDOT’s portion of funding comes from an economic development fund earmarked especially for roadway improvements linked to community economic development. In this case, Edward Jones is pledging the addition of 500 new jobs.
Current project timeline
Public meeting Oct 2007
Open for bids June 2009
Awarded lowest bid July 2009
Construction started spring 2010
Diverging diamond interchange opened October 2010
Construction completion spring 2011
Additional Information:
Proposed I-270 and Dorsett Road Interchange Project (1 page, 2.54 MB)
To view artist's renderings of the interchange enhancements by the city of Maryland Heights, click here (2.83 MB, PDF)
To sign up for email updates on the project, click here