Diverging Diamond Interchange (DDI)

WisDOT has constructed Diverging Diamond Interchanges (DDIs) at several highway interchanges across the state. This alternative interchange, sometimes called a “double crossover diamond,” is designed to intuitively guide motorists through the interchange.

These interchanges have been shown to increase capacity and safety, decrease congestion and minimize the cost of new infrastructure. The DDIs in Wisconsin are located at:

Diverging Diamond Interchange
View a full size photo of a DDI

  • I-39/90 and WIS 11/Avalon Road interchange, south of Janesville
  • WIS 441 and Oneida Street interchange, Appleton
  • I-39/90 and WIS 26/Milton Avenue interchange, Janesville
  • I-39/90 and WIS 81 interchange, Beloit
  • I-43 and Brown Deer Road interchange, Milwaukee County
  • I-41 and WIS 15/Northland Avenue interchange, Appleton
  • I-41 and Ballard Road interchange, Appleton

DDIs are designed to have traffic use directional crossovers on either side of the interchange to guide roadway users through the interchange area to improve left-turning traffic by eliminating the need for left-turning vehicles to cross the vehicle paths of approach through-vehicles. DDIs are generally used when there are heavier left-turning traffic volumes to and from a freeway in existing or planned conditions.

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Benefits of Diverging Diamond Interchanges

  • Safety – Reduces the number of crossing conflicts for vehicles and eliminates the need for left-turning vehicles to cross the paths of approaching through vehicles.
  • Greater capacity and efficiency – Accommodates more traffic than conventional designs. Drivers make free-flow right and left turns on to the major freeway.
  • Easy navigation – Channels drivers into directional crossovers in which they are guided by with overhead signs, pavement marking, and traffic signals.
  • Meets the needs of all road users – Accommodates large trucks, pedestrians and bicyclists.

Diverging Diamond Interchanges improve safety by channelizing all traffic into dedicated lanes to help drivers navigate through the interchange, as well as provide free-flow movements for left-turning vehicles. This free-flow movement eliminates the need for left-turning vehicles to cross paths of the approaching through vehicles. This left-turn movement often results in severe injury crashes, but is eliminated entirely with the DDI design.

When compared to a diamond interchange, DDIs generally have less vehicle conflict points which can improve safety by leading to an overall reduction in crashes and removing some of the most severe types of crashes.

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According to a study in Missouri, Diverging Diamond Interchanges reduce fatal and injury crashes by 63%. Similar results have been observed in Wisconsin with reductions of over 50% in total crashes and 65% in fatal and injury crashes.

WisDOT primarily builds these interchanges where there is existing or anticipated future traffic patterns that have heavier left-turning movements to and from a freeway. A DDI is also evaluated if there is a need for additional roadway capacity due to space or infrastructure limitations. WisDOT considers many factors such as safety, geography, user needs and operations when considering an interchange design for a specific location. View the map to see locations of existing and proposed DDIs.

DDIs channelize roadway users into directional crossovers to safely navigate the interchange area. This movement transitions traffic from the right side of the roadway to the left side and back again. This crossover eliminates the need for left-turning vehicles to cross paths with any opposing through vehicle movements. These movements are accomplished through a series of road design, signs, pavement markings and traffic signals making it a simple, often unnoticed, movement. The general steps to navigate a DDI are as follows:

  • 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 freeway 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.