Are Diverging Diamond Interchanges the Future, or is it Already Outdated?
Diverging Diamond Interchanges are far safer than traditional stops, but with the better designs available, are governments wasting taxpayer money?
Back in the year 2000, an American engineering graduate student was inspired by the former "synchronized split-phasing" type freeway-to-freeway interchange that had once been installed north of Baltimore, and “re-invented” the Diverging Diamond Interchange (DDI). Why does Wikipedia even state that the DDI was re-invented in 2000 by an American? It’s because it was really invented by the French in the 1970s and, evidently, not even Wikipedia wants to give the French credit! (lol) So I guess we Americans will just have to rewrite history here and take credit for it; or will we just get the blame?
DDI via the Spartanburg Area Transportation Study
The Diverging Diamond Interchange (DDI) is a traffic interchange in which two directions of traffic cross the road via a bridge or tunnel to the opposite side by briefly having vehicles crossing and driving on the opposite side of the road, while the perpendicular traffic travels straight through without stopping. The advantage of this system is that you only need two traffic lights for crossing traffic, while the perpendicular traffic is still protected.
DDI via the Florida Squeeze
Traditional four-way intersections have 32 separate opportunities where vehicles can collide into each other. In a DDI, there are only 14 such opportunities. However, DDIs are horrible for foot and bicycle traffic unless specially made pathways are added, at great expense. Also, one has to ask the question, if you’re going to spend the money to build a bridge or tunnel for an interchange, why not just do it right and make it a Continuous-Flow Interchange like every freeway interchange in America? Does a DDI really save that much real-estate?
According to divergingdiamond.com, there are at least eighty-eight (88) DDIs in America right now, with more in development. In the past two weeks alone, DDIs have opened up in Sarasota, Pittsburgh, and Calgary, with another one in Saskatchewan scheduled to open any day now. Here is a video showing how the DDI in Calgary works:
It seems that DDIs are proliferating across America, Canada, France, South Africa, Denmark, Australia, and even the United Arab Emirates (UAE). This is mainly due to the improved safety and because DDIs use far less real-estate than traditional free-flowing interchanges. However, this proliferation of DDIs comes across as a waste of taxpayer money, because there are better alternatives already available.
DDI via Mike on Traffic
The Double Crossover Merging Interchange (DCMI) is a patented free-flowing interchange variant, which includes elements from the diverging diamond interchange, but eliminates the disadvantages of weaving and of merging into the outside lane. DCMIs use virtually an identical amount of land as a DDI, cost nearly the same to construct, have no stop signs or traffic lights, and are even safer.
As of 2016, not a single Double Crossover Merging Interchange (DCMI) has been constructed anywhere on the planet. So why are these massive (DDI) government transportation projects moving forward when better options are available? Could a patent held by an Architect and University Professor be so costly as to stop all consideration by government officials?
What will it take to get governments to stop wasting taxpayer money building inefficient and outdated Diverging Diamond Interchanges, and start implementing the safer and more efficient Double Crossover Merging Interchange?
Keep driving my friends!
My thanks to Larry for all his help with this article!