Eliminating the Dreaded Left Turn

The FHWA says that 40% of all traffic accidents happen at intersections, and many of those are caused by left turns. A new type of intersection called the "diverging diamond" takes left turns out of the picture.

1 minute read

October 12, 2011, 12:00 PM PDT

By Tim Halbur


Slate's Tom Vanderbuilt looks at the left-turn problem, and the solution proposed by Gilbert Chlewicki. Here's how it works:

"As the eastbound driver approaches the highway interchange (whose lanes run north-south), traffic lanes "criss cross" at a traffic signal. The driver will now find himself on the "left" side of the road, where he can either make an unimpeded left turn onto the highway ramp, or cross over again to the right once he has gone under the highway overpass."

Monday, August 1, 2011 in Slate

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

Cover CM Credits, Earn Certificates, Push Your Career Forward

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.

June 18, 2025 - Diana Ionescu

Two people walking away from camera through pedestrian plaza in street in Richmond, Virginia with purple and white city bus moving in background.

Vehicle-related Deaths Drop 29% in Richmond, VA

The seventh year of the city's Vision Zero strategy also cut the number of people killed in alcohol-related crashes by half.

June 17, 2025 - WRIC

Woman and young girl looking at subway map, woman pointing.

Can We Please Give Communities the Design They Deserve?

Often an afterthought, graphic design impacts everything from how we navigate a city to how we feel about it. One designer argues: the people deserve better.

June 9, 2025 - John Pobojewski

Close-up of yellow and black goldspotted oak borer beetle on blade of grass.

Southern Californians Survey Trees for Destructive Oak Pest

Hundreds of volunteers across five counties participated in the first Goldspotted Oak Borer Blitz, surveying oak trees for signs of the invasive beetle and contributing valuable data to help protect Southern California’s native woodlands.

June 22 - UC ANR Green Blog

New five-story apartment building under construction.

Opinion: How Geothermal HVAC Lowers Costs, Improves Grid Resilience

Geothermal heating and cooling systems can reduce energy costs and dramatically improve efficiency.

June 22 - Greater Greater Washington

Close-up on clipboard with pre-tenancy application and red pen.

Tenant Screening: A Billion-Dollar Industry with Little Oversight. What’s Being Done to Protect Renters?

Reports show that the data tenant screening companies use is often riddled with errors and relies on information that has no bearing on whether someone will be a good tenant.

June 22 - Shelterforce Magazine