CBB provided traffic engineering and planning assistance to the Missouri Department of Transportation (MoDOT) for the design and implementation of the I-270 and Dorsett Road Diverging Diamond Interchange (DDI). Following construction in 2010, this was the first DDI in the St. Louis region.
The project included extensive stakeholder and public involvement, VISSIM alternative analyses, and signal timing development and implementation.
Prior to MoDOT selecting the DDI as the preferred concept, CBB evaluated a range of alternate configurations including modified diamonds, partial clover-leafs, roundabouts, and single-point urban diamonds. Based on CBB’s analysis and several engineering factors, MoDOT and its project partners ultimately selected the DDI for construction.
During the construction phase, CBB developed and implemented the unique signal timing required to ensure safe and protected pedestrian accommodations. Since opening, the interchange operates with far less delay, and traffic queues no longer back onto I-270 during the peak periods.