MDOT to build diverging interchange at I-75 and 12 Mile in Madison Heights

Project to begin in late February

Diverging diamond interchange in Oakland County. (Michigan Department of Transportation)

MDOT says it will move ahead with plans to build an innovative interchange at a busy intersection in Madison Heights.

MDOT will build a diverging diamond interchange (DDI) at I-75 and 12 Mile Road after the design was approved by the Federal Highway Administration late last year.

The interchange is part of the ongoing I-75 modernization project in Oakland County. DDIs were recently built at Big Beaver and 14 Mile roads along I-75, and the design is preferred by the Road Commission for Oakland County and the City of Madison Heights.

The rebuilding of 12 Mile Road and the new interchange is expected to begin in late February. During the rebuilding phase, all ramps at the interchange will be closed and through-traffic on 12 Mile Road will be detoured between Stephenson Highway and Dartmouth Street. Access to businesses will be maintained on each side of the interchange.

Related: Community pushing for changes to ‘dangerous intersection’ in Birmingham

So what exactly will the DDI look like and what’re the benefits?

A DDI is 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 blueprint. (MDOT)

Here’s a video showing how it works:

Safety Benefits:

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

Operational Benefits

  • Provides 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).
  • Allows simple left and right turns from all directions.
  • Increases the number of left-turning vehicles without the need for additional lanes.
  • There is more space between the signalized intersections at the ramps and one less signal.

Cost-Effective Solution

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

More: Oakland County news

About the Author:

Ken Haddad is the digital content and audience manager for WDIV / He also authors the Morning Report Newsletter and various other newsletters. He's been with WDIV since 2013. He enjoys suffering through Lions games on Sundays in the fall.