The Diverging Diamond

Last week I lamented that nobody is concerned with the gains from improved traffic management. Right on cue, as if they were waiting to refute my complaint, the Chicago Tribune introduces us to the “diverging  diamond interchange” (DDI).  Although the design temporarily requires traffic to drive on the left side of the road, it’s better than that of standard diamond interchanges  in almost every way.

A DDI allows traffic getting on and off an expressway to flow freely without stopping or yielding to other vehicles. It’s also considered safer and often cheaper to build than standard diamond interchanges. Experts say DDIs have fewer “conflict points” — a technical term for places where crashes can occur — than standard interchanges.

Sounds like a resounding success for our ability to innovate, right? Well, not so much.

Saiko said Versailles, France, has used the design since the 1970s. So why, after decades of building interstates and expressways, did it take so long for the concept to reach the U.S.?

Highway designers and engineers are wary of taking any chances with millions of dollars of public money at stake, Saiko theorized. “Nobody (in the U.S.) wanted to be the first to try it. Nobody wants to be the guinea pig,” he said.

When public dollars are at stake a low-risk, high-reward option still entail too much risk. The Obama administration has laudably been more apt to play “science lab” with public money, but at the state level where most of these types of decisions are made it’s nearly impossible.

Hopefully the DDI will be successful in America and lead to more experimentation in the future.  Infrastructure innovation is one of the few areas where there is still low hanging fruit in terms of  implementing ideas from other parts of the world.


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