On the Rise of the Diverging Diamond Interchange

Its design can appear baffling at first, but the DDI presents drivers with far fewer opportunities to collide with each other than traditional four-way intersections.

1 minute read

September 18, 2017, 9:00 AM PDT

By Philip Rojc @PhilipRojc


Diamond Interchange

KOMUnews / Flickr

Laura Bliss covers the spread of the diverging diamond interchange, or DDI. "Rather [than] 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."

Bliss includes an embedded Youtube video from the city of Calgary, which cheerily explains how drivers should use a DDI.

"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." They can also incorporate pedestrian crossings, as the Calgary video shows. 

Monday, August 21, 2017 in CityLab

portrait of professional woman

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching. Mary G., Urban Planner

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching.

Mary G., Urban Planner

Use Code 25for25 at checkout for 25% off an annual plan!

Redlining map of Oakland and Berkeley.

Rethinking Redlining

For decades we have blamed 100-year-old maps for the patterns of spatial racial inequity that persist in American cities today. An esteemed researcher says: we’ve got it all wrong.

May 15, 2025 - Alan Mallach

Logo for Planetizen Federal Action Tracker with black and white image of U.S. Capitol with water ripple overlay.

Planetizen Federal Action Tracker

A weekly monitor of how Trump’s orders and actions are impacting planners and planning in America.

May 21, 2025 - Diana Ionescu

Rendering of California High-Speed Rail station with bullet train.

California High-Speed Rail's Plan to Right Itself

The railroad's new CEO thinks he can get the project back on track. The stars will need to align this summer.

May 19, 2025 - Benjamin Schneider

Red SF Muni ticketing machine.

San Francisco Muni Raises Fares a Second Time

A 10–cent fare hike for adults is part of the agency’s plan to chip away at a growing budget deficit.

5 hours ago - San Francisco Examiner

Electric car charging station with several Chevy Bolts charging in parking lot of store in Bellingham, Washington

Electric Grid Capacity Could Hamstring EV Growth

Industry leaders say the U.S. electric grid is unprepared for the increased demand for power created by electric cars, data centers, and electric homes.

6 hours ago - GovTech

Top view new development riverside residential and commercial neighborhood with vacant land in Texas, USA.

Texas Bill Supports Adaptive Reuse in Commercial Areas

Senate Bill 840, which was preliminarily approved by the state House, would allow residential construction in areas previously zoned for offices and commercial uses.

7 hours ago - The Texas Tribune