Travel I-75

Project Highlights - DDI Edition

What is a Diverging Diamond Interchange (DDI)?

A Diverging Diamond Interchange is:

    • An innovative interchange design that improves safety and mobility.
    • Similar to a conventional diamond interchange, which is the most common in the United States, where the exit/entrance ramps make a diamond shape between the freeway and surface street. Right-hand turns are handled the same at both a DDI and a diamond interchange.
    • Different in how it handles left turns, since:
      • The intersections with the freeway ramps smoothly move traffic on the surface street from the right side of the roadway to the left side of the roadway as the road crosses the freeway.
      • Traffic is on the left-hand side of the roadway between the signals at ramp intersections, all left turns occur at the entrance/exit ramps without having to cross opposing traffic.
    • Road geometry, signs, and pavement markings working together to make driving through the DDI very simple.

DDI’s are currently located along I-75 at 14 Mile and Big Beaver Roads in Troy and at University Drive in Auburn Hills.

Federal Highway Administration (FHWA) on Alternative Intersections: Diverging Diamond Interchange video (7:39) 

Interchange Examples:

Graphic showing existing Big Beaver Road Interchange flow of traffic

Flow of traffic in previous Big Beaver Road configuration


Graphic showing flow of traffic in a Diamond Interchange

Flow of traffic in a typical Diamond Interchange configuration


Graphic showing flow of traffic in a Diverging Diamond Interchange.

Flow of traffic in a Diverging Diamond Interchange configuration

Where did DDIs go in?

Three were planned to go in as part of this project:

  • Big Beaver Road opened in late spring 2021
  • 14 Mile Road opened in fall 2021
  • 12 Mile Road opened in the summer of 2023 
  • An existing DDI design is located on I-75 at University Drive in Auburn Hills. The difference is in the location of the interchange; at University Drive, the DDI is located above I-75, and the new DDI’s have road located below the freeway.

Aerial graphic with indicators of proposed changes to interchange

Why did we need DDI’s as part of this project?

DDI’s helped facilitate safer movement for vehicles, pedestrians, and cyclists while increasing throughput.  

Safety Benefits:

  • Reduced conflict points between vehicles and non-motorists by nearly 50 percent.
  • Eliminated many of the most severe crashes, which happen at right-angles.
  • Increased visibility for drivers turning.
  • Reduced potential of people driving the wrong way on entry ramps.
  • Separated non-motorized users (bikes and pedestrians) by routing them through the median or along the sides of the roadway.
  • Simplified crosswalks and involves crossing fewer lanes at a time.

Operational Benefits

  • Provided a simple two-phase signal design with shorter cycle lengths (total time for the traffic signal to give a green light for ramp traffic and a green light for the surface street traffic).
  • Allowed simple left and right turns from all directions.
  • Increased the number of left-turning vehicles without the need for additional lanes.
  • There was more space between the signalized intersections at the ramps and one less signal.

Cost-Effective Solution

  • Reduced the construction cost compared to other interchange forms.
  • Required fewer lanes therefore, existing bridges and right-of-way can be utilized.
  • Utilized a smaller project footprint, which means fewer impacts to adjacent areas.

How do you navigate a DDI and what to expect?

In Cities where DDIs have been built, drivers say they do not even notice the crossover intersections (shifting to the left side of the road). This can be attributed to the road geometry, signs, and pavement markings that make navigating a DDI easy for the driver. With reconstruction complete at Big Beaver Road and 14 Mile Road you may have already experienced navigating a DDI, if not you can view this short video for a glimpse of how this type of interchange works. 

How to drive a DDI (1:11 with audio)

Below were the four travel paths made within a DDI: Through, left turns onto I-75, left turns from I-75, and right turns to/from I-75.

Some Additional Example Videos/Resources

Project Videos

12 Mile Road - October 2022

12 Mile Road - May 2022

14 Mile & Big Beaver Roads - December 2020