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I-39/90 Expansion Project

Illinois state line to Madison, Dane and Rock counties

Diverging Diamond Interchange

Wisconsin’s first Diverging Diamond Interchange (DDI) was completed in November 2016 at the I-39/90 and WIS 11 (Avalon Road) interchange (Exit 177), south of Janesville, as part of the I-39/90 Expansion Project between Madison and Beloit. In addition, the interchanges at WIS 26 (Exit 171A) in Janesville and WIS 81 (Exit 185) in Beloit will be reconstructed incorporating the DDI design to improve traffic flow.

The Wisconsin Department of Transportation is considering the use of a DDI at other key highway interchanges across the state. This innovative interchange, sometimes called a “double crossover diamond,” is designed to intuitively guide motorists through the pathways. These interchanges have been shown to increase capacity and safety, decrease congestion and minimize the cost of new infrastructure.

Advantages of a DDI

  • Safety – Reduces the number of ways vehicles can collide by almost half (14 compared to 26 for a conventional diamond interchange).
  • Greater capacity and efficiency – Accommodates more traffic than conventional designs. Drivers make free-flow right and left turns onto the major freeway.
  • Easy navigation – Guides drivers with overhead signs, pavement marking, and traffic signals.
  • Meets the needs of all road users – Accommodates large trucks, vehicles, pedestrians and bicyclists.

Navigating a DDI

  • Drivers follow the signs, signals and pavement markings to cross through the intersection at the first set of traffic lights. Traffic appears as if on a one-way street.
  • All left turns onto the freeway are free flow, meaning vehicles do not have to stop to access the ramp.
  • Vehicles going straight simply proceed through a second set of traffic lights.
  • Pedestrians travel on designated walkways and cross only at the crosswalks.
  • Bicyclists may choose to use the bike lane or pedestrian walkways and crosswalks.

DDIs planned for I-39/90 Expansion Project

Currently, DDIs will be constructed at the following interchanges along I-39/90, between Beloit and Madison: