It’s one of the biggest innovations of the past decade. If it hasn’t impacted your life, it soon will. Remarkably, this breakthrough has nothing to do with computers, the Internet or biotechnology.
It’s the “diverging diamond” interchange, a road design that is improving safety and traffic flow at major Interstate intersections around the country.
The DDI improves safety by making it possible to reach interstate on-ramps without making a left-hand turn across oncoming traffic. That’s accomplished by having one or more dedicated lanes shift from the right side to the left side of the overpass and dump traffic onto the ramp. The design also makes it difficult for drivers to get on the ramps going the wrong direction, which is actually a huge problem. A major intersection outside Springfield, Missouri saw a 60% reduction in collisions in the first five months after a DDI was installed.
The traffic lights required to manage the DDI system require shorter cycles, which helps speed the flow of cars.
The first DDI in the U.S. debuted in 2009. There are currently about 60 in active use around the country, with more in the planning stages. It is becoming the preferred design to replace existing interstate intersections.
The DDI does have some limitations. First, there is an awkward start-up period while drivers learn how the system works. It’s not particularly intuitive as you find yourself driving on the left side of the road for part of your movement through the DDI. There’s a DDI intersection near my Atlanta home, and I have to say my first couple of times passing through it were very disconcerting!
The DDI design, with those multiple dedicated lanes, eats up a lot of room, making it impractical for use in cities. And if you miss your turn at a DDI, it can take quite a bit of time and distance to get back on track. But the DDI design and the hard-to-miss road markings it employs greatly reduce the chance of such miscues.
Interesting side note on American exceptionalism. Fortune magazine notes that the DDI appears to be a rare technology that was developed independently twice. An American graduate student named Gilbert Chlewicki came up with the DDI in 2000 for his master’s thesis in transportation engineering. Shortly after, he discovered the design had been in use in France for some time. But Chlewicki, in typical American fashion, started a consulting firm and aggressively promoted the DDI across the country, leading to its adoption as the new gold standard for interstate intersections.
I love that story. So many giants of American industry from Thomas Edison to Henry Ford to Steve Jobs have been more than just innovators, more than just salesmen. They were evangelists. Their passion, as much as their technical know-how, made them wealthy and changed our daily lives.
Only in America!