David Bailey

Left Turns


The US likes center turn lanes. They provide median space to help reduce head-on collisions and, they allow for left turning vehicles to move out of the way of through traffic when waiting for a break in oncoming traffic. However, these lanes use quite a bit of road space because they are rarely used and they encourage speeding by widening the perceived road space. Narrower raised medians or center running light rail tracks can provide the same safety benefits with better use of space.

A typical 5-lane street with a center turn lane
A typical 5-lane street with a center turn lane

In the case of raised medians, a narrower median often allows for a bike lane on either side of the road. This "lane diet" is similar to a road diet. In the case of light rail tracks, it is common for cities to prohibit left turns across light rail tracks to prevent car-train crashes. For example, Santa Monica prohibits left turns across Expo Line tracks on Colorado Avenue. This configuration requires drivers to travel over a mile before being able to turn. Many drivers ignore these restrictions and turn in front of trains. Sometimes this causes train-car collisions. An alternate configuration that allows left turns at all intersections is to create a new, exclusive signal phase for trains and parallel pedestrians. This configuration, popular in Munich, Germany, provides a safer intersection because all vehicle traffic is required to stop for the train. Also, the width of the tracks provides a space for a now-legal left turning vehicle to wait for a break in oncoming traffic without disrupting through traffic.

Currently trains and cars travel through the intersection together. Cars are prohibited from making left turns.
Currently trains and cars travel through the intersection together. Cars are prohibited from making left turns.

Last, I must note that some fire departments may raise concerns about this configuration because they use center turn lanes when responding to emergencies. However I hope these safety conscious departments would appreciate the increased safety benefits of this configuration.


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