In November 2016, the Wisconsin Department of Transportation completed Wisconsin’s first Diverging Diamond Interchange (DDI) at the I-39/90 and WIS 11 (Avalon Road) interchange (Exit 177), south of Janesville.
Why build a DDI at the I-39/90 and WIS 11 (Avalon Road) interchange?
WIS 11 (Avalon Road) has a significant amount of traffic, particularly large trucks, making left turns onto the Interstate. During the morning peak hours, an average of 350 vehicles merged onto I-39/90 northbound from WIS 11 eastbound compared to only 71 vehicles continuing to Avalon Road.
Due to the high volume of left turns onto the Interstate, the previous diamond interchange design was not efficient at reducing traffic congestion and bottlenecks. The DDI design improves traffic flow by creating a free flow left turn, which also improves other congestion related issues including the amount of vehicles waiting behind a vehicle making a turn, traffic synchronization and bottlenecks.