What is a diverging diamond interchange?
The diverging diamond interchange (DDI) is a new type of interchange traffic solution. It has not been constructed in the United States, but a DDI has been proposed by the Missouri Department of Transportation at Interstate 435 and Front Street in Kansas City. The diverging diamond interchange has been used in France.
The Federal Highway Administration has been advocating innovative intersection designs as a way to increase capacity, decrease congestion and minimize the cost of new infrastructure.
How does the DDI work?
The diverging diamond interchange allows free left turns for motorists, meaning vehicles don’t cross opposing traffic. Traffic models indicate this type of interchange works well with areas of heavy traffic.
Examples of how the DDI works can be seen in the following animations below. The first animation involves an aerial view of a simulated DDI. The second animation is from the driver’s view using the I-435 and Front Street interchange.
Overhead view animation of Diverging Diamond Interchange (9.09 MB)
Driver's view animation of Diverging Diamond Interchange (22.6 MB)
How is the DDI better than a traditional interchange?
Because the DDI does not have any left turns that must clear opposing traffic, the design can improve traffic movement with more green time. It will move traffic faster, reduce congestion, and increase safety.
With the help of public input by citizens of Maryland Heights, MoDOT has chosen the diverging diamond interchange option for the intersection of Interstate 270 and Dorsett Road. The DDI will help with current heavy traffic volumes. It is also less costly to build than conventional diamond interchanges.
Who do I contact for more information?
Contact North St. Louis County area engineer Larry Welty at 1-888-ASK MODOT (275-6636) or email Lawrence.Welty@modot.mo.gov
Contact Community Relations Specialist Jack Wang at 1-888-ASK MODOT (275-6636) or email Jack.Wang@modot.mo.gov
