Travel I-75

Project Highlights - DDI Edition

Big Beaver and 14 Mile Road Interchanges UPDATE (November 19, 2020)

As crews are wrapping up work throughout the project for the winter, there is still much that will continue.  Work to complete the Diverging Diamond Interchanges (DDI) at Big Beaver and 14 Mile Roads has made a lot of progress, however Big Beaver DDI is looking to fully open in late December 2020 and the 14 Mile Road DDI is looking to fully open in Spring 2021.  Please see below for an update on each location:

Big Beaver DDI:

Prior to the modernization project, traffic heading to eastbound or westbound Big Beaver Road from either direction of I-75 were using an access road adjacent to the mainline freeway with separate loop ramp exits. The new interchange design eliminates the access roads and combines those separate exit ramps into one exit that provides a direct connection to eastbound or westbound Big Beaver Road.  By mid-December, the interchange is expected to be fully operational. Currently, Big Beaver Road has one lane open in each direction until the interchange is fully operational.  

In the meantime, all northbound I-75 traffic exiting Big Beaver Road will be required to head east. If northbound I-75 traffic needs to go west, traffic will turn right (east) and then utilize the first median turnaround to head westbound. All southbound I-75 traffic exiting Big Beaver Road will be required to head west. If southbound I-75 traffic needs to go east, traffic will turn right (west) and then utilize the first median turnaround to head eastbound.   

14 Mile Road DDI:

Prior to the modernization project, there were separate exits for the eastbound and westbound 14 Mile Road from both directions of I-75. The new interchange design combines those separate exit ramps into one exit that provides a direct connection to eastbound or westbound 14 Mile Road. For the new interchange to operate properly, new signals need to be installed at the crossovers on 14 Mile Road and will be synced (timed) with other signals along 14 Mile Road.

These signal installations and upgrades are expected to occur in spring 2021. Currently, eastbound and westbound 14 Mile has one lane open until these upgrades are completed.

In the meantime, when exiting northbound I-75 at 14 Mile Road, all traffic will be required to turn right (heading east); westbound traffic will use the median turnaround located just before the Oakland Mall parking lot.

When exiting southbound I-75 to 14 Mile Road, all traffic will be required to turn right (heading west); eastbound 14 Mile traffic will be directed to northbound Stephenson Highway to the first median turn around to southbound Stephenson Highway. On southbound Stephenson Highway, traffic will utilize the first median turnaround south of 14 Mile Road and then use northbound Stephenson Highway to turn right (head east) on 14 Mile Road.

We appreciate your patience as the modernization project north of 13 Mile Road continues to make progress towards completion in 2021.

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.

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 existing 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

Proposed Big Beaver Interchange with identifiers for directional crossover movements, left turn movements, and ramp merges

Graphic: Proposed Big Beaver Interchange crossovers, turns, and ramp merges.

Where are DDIs going in?

Two are approved to go in at the I-75/Big Beaver Road and I-75/14 Mile Road Interchanges. 

  • 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 will have road located below the freeway.

Proposed I-75 at Big Beaver Interchange video (1:44 no audio)

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

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

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.

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. Below are 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