What’s the flow?

Q&A with Sharon Peters

Q: They’re constructing a new intersection and traffic flow setup at the highway that intersects the interstate. It’s called a diverging diamond interchange. A diagram was in the paper, and it looked like a tangle of crossovers, raising more questions than it answered. Do you know anything about this approach? Does it exist anywhere else or are we going to be the guinea pigs for some convoluted mess that resembles a snowmobile track?

A: The diverging diamond interchange (DDI) is coming to my town, too, and early reaction here is nervous horror. The diagrams do make the thing look almost impossible to maneuver.

I haven’t driven on one. I can tell you this: The first was constructed in Springfield, Mo. in 2009, and was regarded as sufficiently effective in reducing traffic backups and accidents that by the end of 2010, that state had two more DDIs. There are still only a relative handful in this country (in New York, Utah and Colorado, among others), but scores are in the planning or construction stages.

The routing of these DDIs requires drivers to follow a traffic pattern we’re not accustomed to so as to allow for “free left turns,” meaning we don’t have to cross across oncoming lanes of traffic (as we do now) to make a left turn (onto an interstate entrance ramp).

Diagrams of DDIs don’t clearly articulate how they work, nor do words. There’s a YouTube video that demonstrate traffic movement on DDIs which, better than anything, shows how you’d move through these things. Go to YouTube and type in “DDI animation.” You’ll have to bypass a few video titles on weapons until you get to one that’s clearly about interchange design.

Among the upsides of the DDIs listed by proponents: Fewer “conflict points” (places where vehicles can have unpleasant adventures), virtually no way for drivers to become confused (despite what most of us are thinking at this point), and it’s almost impossible for drivers to go onto the wrong entry ramps and wind up heading the wrong way on the interstate. One study showed that 97 percent of drivers felt the DDI in Springfield was safer than the previous interchange.

We’ll adjust!

© CTW Features

What’s your question? Sharon Peters would like to hear about what’s on your mind when it comes to caring for, driving and repairing your vehicle. Email [email protected].