What is the Diverging Diamond Interchange?

You’ve probably heard about this type of interchange in some US states. It’s coming to Florida and will be at select intersections.

Currently, one is being constructed in Sarasota at the intersection of Interstate 75 and University Parkway.

What is a Diverging Diamond Interchange?

A Diverging Diamond Interchange allows traffic on a secondary street to cross to opposite sides of the road.  The design allows for no left turns across oncoming traffic.

Another feature is a reduction in the number of traffic light cycles.

Rendering of future Diverging Diamond Interchange in Sarastota, Fla. Source: FDOT
Rendering of future Diverging Diamond Interchange in Sarasota, Fla.

According to the website DDI, the first interchange in the United States opened in June of 2009 in Springfield, Missouri.

Popular Science named the Diverging Diamond Interchange one of the 100 Best Innovations of 2009.

Approximately 70 interchanges currently exist in the United States.  All 48 contiguous states either have present or planned interchanges.

The main objective is to allow for a greater flow of traffic on secondary roads.  This will, in turn, allow primary highways to move faster, as ramps will be less likely to back up.

Origins

Similar intersections were first built in France in the 1970s.  Around 2000, engineers brought up the idea in the United States.

In 2003, Transportation Engineer Gilbert Chlewicki wrote a paper discussing the possibility in detail.

What are the Advantages?

  • Larger radius curves allow for greater visibility and fewer off-road collisions
  • No left turns across traffic will allow for traffic to move more smoothly onto ramps.  A left turn will be a merge into the nearest lane of travel instead of crossing traffic and accessing the farthest lane of travel.
  • Fewer traffic lights and fewer situations of cars crossing traffic will prevent accidents.
  • No need for dedicated left or right turn lanes.  Space can be used either for pedestrian traffic, bike lanes, or additional travel lanes.  Though some turn lanes may be installed, most turns will be shared with thru traffic.

What are the Disadvantages?

  • Pedestrian traffic will have more lanes of travel to cross, including the paralleling road twice.
  • There is no easy way to exit the main highway and quickly re-enter, in the event of an accident on the overpass.
  • Both directions of traffic on the secondary road cannot flow freely at the same time, due to the paralleling lanes crossing each other at two different locations.
  • Some drivers could get confused by being on the “wrong side of the road;” drivers used to oncoming traffic being on the left.  Landscaping and wide medians seem to have made this fear insignificant.

Adjustments to Existing Intersections.

  • Re-striping of travel lanes.
  • Updated medians and islands.
  • New signage, in order to avoid the confusion coming with a new interchange alignment.
  • Re-positioning and re-timing of new traffic lights.

Is it Worth It?

In any areas with a massive combination of entering/exiting traffic and congested secondary streets, absolutely.

Construction of a Diverging Diamond Interchange is necessary also in areas anticipating a massive amount of growth.

Along new limited-access highways, look for these interchanges more and more in the coming years.

 

What are you thoughts on the Diverging Diamond Interchange?  Please comment in the box below.

 

 

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