Centreline hardening strategies are a form of traffic calming intended to make intersections safer for pedestrians by reducing the turning radius for motor vehicles. The use of physical objects such as bollards, delineators or rubber curbs encourage drivers to make left turns at slower speeds.


Address pedestrian risk at signalized intersections by attempting to reduce vehicle speeds during left turns.


In an effort to find effective ways for improving pedestrian safety outcomes, the City of Calgary identified that reductions in vehicle speeds appear to consistently achieve progress toward these goals. In addition, collision data from the City of Calgary from 2008 to 2012 indicates that most collisions involving pedestrians occur at signalized intersections and predominantly involve left-turning vehicles. Left-turning vehicles were found to represent the highest single contributor toward serious and fatal injury collisions.

In light of this information, the city identified centreline hardening strategies as a potential solution. The city cites findings from New York City’s Turn Calming Program, a citywide effort to reduce left and right turn speeds and enforce safe turning behaviour as a part of the city’s Vision Zero initiative. The NYC Department of Transportation (2021) indicates that basic hardened centrelines have been installed at more than 300 treatment locations since 2016.

Centreline hardening treatments will be installed at three to five signalized intersections throughout Calgary. Currently, the city is developing a detailed methodology for the project. Potential treatment sites are being investigated to identify locations based on historical pedestrian-vehicle collision issues. Preference for the treatments will be given to locations with severe collision outcomes and higher speeds.

Data and lessons learned

Reducing the speed of left-turning vehicles is expected to significantly improve collision outcomes. Data and lessons learned will be provided as findings from the pilot become available.

According to the NYC Department of Transportation (2021), pedestrian injuries at New York City intersections have decreased by 20 per cent where Turn Calming treatments were implemented. Additional results from Turn Calming locations include:

  • Median left-turn speeds have decreased by 54.3 per cent
  • Average left-turn speeds have decreased by 52.6 per cent
  • 85th percentile left-turn speeds have decreased by 59.8 per cent
  • Maximum left-turn speeds have decreased by 37.7 per cent

Vehicles were found to be making safer turns as well; the rate of crossing the double yellow line while turning has dropped by 78.9 per cent for locations that have a treatment extending to the stop bar and 100 per cent for locations that have a treatment extending all the way to the crosswalk.

Using data collected in Washington D.C., Hu & Cicchino (2020) examined how hardened-centreline treatments affected the number of conflicts between left-turning vehicles and pedestrians as well as left-turn speeds at intersections. They compared areas where the treatment was installed with control intersections without treatment, both before and after installation. The treatment had the following effects:

  • Conflicts between left-turning vehicles and pedestrians reduced by 70.5 per cent
  • Mean left-turn speeds reduced by 9.8 per cent
  • Odds of left-turning vehicles exceeding 15 mph reduced by 67.1 per cent

The study concludes that hardened-centreline treatment can reduce conflicts between left-turning vehicles and pedestrians, and slow down left-turning traffic at intersections.

Next steps

The treatment installations are expected to take place in spring 2021. Data collected for analysis will likely include vehicle speeds, collisions and/or pedestrian-vehicle conflicts, and the frequency of vehicles crossing the yellow centreline.