Drivers may be baffled by these newfangled intersections, but they’re safer than traditional four-way stops.

End-of-summer road trippers: Get ready to merge like never before. Diverging diamond interchanges are coming to a highway near you.

The brainchild of an engineering graduate student in the early 2000s, diverging diamond interchanges, or DDIs, work rather ingeniously. Rather make drivers turn at a right angle to merge onto a highway, the two directions of traffic diverge and ribbon over one another. One lane peels off to funnel cars onto the highway, and they never have to turn against traffic.

In the past two weeks alone, Florida opened all 12 lanes of the nation's largest DDI near Sarastota. Near Pittsburgh, a brand new DNA-shaped interchange is confusing some Pennsylvania drivers and delighting others. Southeast Calgary opened another one this week, Saskatchewan awaits its own, there’s news that Arizona and Virginia are considering proposals to build out more. Here’s a full list of nearly 90 U.S. locations where they’re planned or operational.

DDIs are proliferating because they’re safer than a traditional four-way intersection. Where two, two-lane roadways intersect, drivers have 32 separate opportunities to collide into each other. In a DDI, there are only 14. The DDI in Springfield, Missouri—the first in the U.S.—showed a 60 percent reduction in crashes since it was installed in 2009, compared to the old design. They can also be more cost-efficient than traditional diamond interchanges.

Urbanists might grump that there’s no such thing as a “good” highway onramp, but some DDIs come with walking and biking paths alongside the twisting lanes (separated, of course), with engineers applauding themselves for the freer flow of feet and bikes created. (‘Cause if cars don’t need to stop for traffic, neither do people.) And with traffic fatalities rising at alarming rates and funding to rebuild decaying roads getting tighter, the DDI seems like a positive trend for both drivers and DOTs. "Human beings, I know, hate change,” Pennsylvania Governor Tom Wolf said on the occasion of his state’s first. “But this really works.”

About the Author

Most Popular

  1. Life

    At Atlanta’s Rail Stations, a Transit-Oriented Soccer League Takes Shape

    Swaths of empty space at train stations are being turned into athletic fields for kids and adults.

  2. Design

    Lisbon’s Beautiful, Dangerous Sidewalks

    The artistic and slippery “Portuguese pavement” has become Lisbon’s calling card. City Hall wants to replace a few stretches of them with concrete—a seemingly sensible decision that has sparked outrage.

  3. Transportation

    Beverly Hills Has Financed Its Metro Fight With $13 Million In Local Taxes

    Instead of reconstructing aging school facilities, the district is using a voter-backed ballot measure to pay for a legal campaign against a subway extension.

  4. Two men shake hands across a table at a job fair.
    Life

    Wages Are Higher in Urban Areas, But Growing Faster in Rural Ones

    The picture of wages and salaries across the U.S. is not a simple one of urban success versus rural decline.

  5. A vacant home on Milwaukee's north side.
    Equity

    Can Milwaukee Really Create 10,000 Affordable Homes?

    The city has an ambitious plan to fix its housing woes. But so far, most of development has been focused on the city’s downtown area.