Left Turn Traffic Calming

Left Turn Traffic Calming

Left Turn Traffic Calming (LTTC) treatments are simple intersection upgrades that boost pedestrian safety and result in safter turning behaviors from drivers. These projects enable CDOT to address crash trends at intersections. In Chicago between 2017 to 2021 left turning motorists were involved in 40% of crashes where a pedestrian was severely injured or killed at an intersection.

How it Works

LTTC treatments “harden” the centerline at an intersection with raised curbs, bollards, and rubber speed bumps. Some locations may call for a rubber speed bump extending into the intersection or shortened pedestrian crossing distances with paint-and-post curb extensions.

This design discourages left turning drivers from cutting across the centerline, guiding them to turn at a safer angle with slower speeds and better visibility of people walking. This way, drivers more intuitively complete their left turns within the safe turning zone, reducing conflicts with pedestrians.

A Focus on Left Turns

Reducing traffic crashes is an urgent matter for CDOT. In 2021, more than 500 people were seriously injured or killed in traffic crashes while walking in Chicago. Between 2017 and 2021, left turning motorists were involved in 40% of crashes where a pedestrian was severely injured or killed at an intersection. Left turns are more complex than right turns. Drivers must search for gaps in oncoming traffic, pedestrians can be blocked from view by the vehicle’s “A-pillar”, and the wider turning path enables higher speeds.

View of intersection with cars traveling through it. Left Turning motorists must search for gaps in oncoming traffic.
Complex Maneuvers
View from inside of a car showing a person walking and the car frame. Pedestrians obscured by vehicle
Low Visibility
View of intersections with person walking in crosswalk and left turning vehicle yielding. High Speed turns. Greater exposure for pedestrians in the crosswalk.
Wider Turning Paths
Measuring Success

CDOT has installed LTTC at 18 intersections across the city, including neighborhoods such as Belmont Cragin, Englewood, Humboldt Park, and Ravenswood. Observations at eight pilot locations showed 97% of vehicles turning within the Safe Turning Zone, up from 73% before the installations.

Diagram of intersection before installation of left turn traffic calming displaying the vehicle turning path cutting through a large portion of the crosswalk. Wide turns enable dangerous speeds and reduce visibility.
Before Installation
Diagram of intersection after installation of left turn traffic calming displaying the vehicle turning path cutting around the rubber speed bump. Tighter turns mean safer speeds and better visibility.
After Installation
Portion of drivers yielding to people walking

Before installation:

73%

After installation:

94%

Portion of drivers turning within the safe zone:

Before installation:

73%

After installation:

97%

Reduction in left turn crashes on state street:

24%

 

Reduction in all crashes on state street:

24% 

Where to Find It

CDOT has installed LTTC at 18 intersections across the city, including neighborhoods such as River North, Belmont Cragin, Englewood, Humboldt Park, and Ravenswood. Dozens more locations are targeted for installation in 2023.

Image: 71st St and Ashland Ave

Additional Resources