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Toronto’s Vision Zero Before-After Evaluation of a Left Turn Calming Pilot

Author(s): Hallett, Samara

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Abstract:

Context:

In Toronto, collisions at intersections between left turning vehicles and pedestrians account for about 18% of pedestrians being killed or seriously injured. Toronto’s Vision Zero program aims to bring this number down to zero fatalities.

There are a number of contributing factors to why left turn collisions are overrepresented in severity vs. right turning collisions:
• High vehicle turning speeds due to longer acceleration distance (i.e. compared to a right turn).
• Large area of pedestrian exposure in the crosswalk due to driver angle of approach.
• Driver workload due to having to wait for (and judge) gaps in oncoming traffic and crossing pedestrians, often with "back pressure" from vehicles behind the turning vehicle.
• Obscured visibility of pedestrian due to vehicle's A-pillar.

Left turn calming measures force drivers to take a sharper turn (much like curb radii reductions for right turns). Sharper turns reduce vehicle speed and bring the angle of approach closer to 90 degrees, which in turn provides better sightlines between vehicles and pedestrians. There are a few other tools to reduce this conflict (i.e. Leading Pedestrian Intervals, fully protected turns, turn prohibitions), but they usually come with impacts to intersection capacity.

To help reduce incidents and fatalities, Toronto’s Vision Zero team believes that reducing the speed of left turning vehicles and improving sightlines may contribute to the goal. Toronto therefore decided to conduct a pilot project at 10 intersections wherein they will implement treatments (such as speed bumps/humps and bollards) to slow down left turning vehicles and improve sightlines. The City then wishes to study the effectiveness of these treatments immediately after they are implemented, (vs. waiting for the collection of collision data over the coming years). A video-based surrogate safety analysis will therefore be conducted to compare vehicle speeds, frequency and severity of interactions between drivers and pedestrians at each location. Preliminary research in the field of automated surrogate safety analysis already indicates that conflicts are a strong predictor of future crashes and can help cities like Toronto better understand road user behaviour in an effort to diagnose safety challenges on roadways, and then effectively measure any improvements made without depending solely on crash data.

Objectives:

To evaluate the effectiveness of a pilot project intended to slow down left turning vehicles and reduce conflicts with pedestrians at 10 intersections using video-based surrogate safety methods.

Target Group:

While the pilot project itself is targeted at improving road safety for pedestrians, drivers might also experience safety benefits out of improved sightlines and reduced speeds.

This presentation is targeted at transportation and road safety practitioners across Canada hoping to gain insight from the left turn calming pilot in Toronto, while learning about advanced and affordable methods of evaluating countermeasure treatments at any road segment using video/traffic cameras.

Activity(ies):

1. To assess this countermeasure’s effectiveness, a pilot project will be conducted in two phases, (Before and After) with the aid of Transoft Solutions’ video-based surrogate safety analysis application. In both phases, cameras will be installed at each of the 10 intersections and video data will be collected for 2 days to obtain traffic flowing through the intersections, with special emphasis on pedestrians. After the Before video collection is completed, Toronto will install left turn calming treatments such as speed bumps/humps and bollards at the 10 intersections.

2. Once the calming measures have been installed, the After phase will commence. Cameras will be installed at the same 10 locations and video will be collected for another 2 days. The video data will then be processed to provide the same safety and traffic metrics as were provided in the Before phase.

3. The Before and After surrogate safety metrics will then be compared to assess whether vehicle speeds and/or unsafe road user interactions decreased after the treatments were installed.

Deliverables:

The below automatically generated outputs will be analyzed Before (March) and then again After (May) the treatments are installed at each site. A detailed comparative study will be completed to assess the effectiveness of the treatments at each site. Outputs includes:

Conflicts/Near-misses: Data and graphs depicting safety indicator values, road user types, road speeds and conflict speeds, road user movements, road user arrival patterns, time and date of events. Conflict videos for all events below the City’s desired design safety margin will also be reviewed.

Speeding: Data and graphs depicting road user speed by type, movement, date and time, as well as road user excessive speeding and road user conflicting speeds (if involved in conflict). Speed distribution by movement, speed distribution by road user, and temporal variation of speed. Speeding event video clips for all road users exceeding the maximum indicated speed value will also be reviewed.

Volumes: Data and graphs depicting road user counts by type, movement, date and time, as well as average/cumulative 15- minute counts by turning movement.

**While the results of this study were not available at the time this abstract was due (March 1, 2021), they will be available May 2021. The outcome of this study will be meaningful to the City of Toronto regardless of whether the comparative study shows that speeds and/or high-risk interactions
i) decreased, ii) remained the same, or iii) increased after the treatments were implemented. If significant decreases in speed and/or conflicts are observed in the after period, then the City might declare the pilot successful and roll out these treatments permanently and/or at additional locations. If speeds and/or conflicts do not change significantly from the Before to After period, then the City might consider collecting additional video during the summer months or decide that the benefits of rolling out such treatments do not outweigh the costs. Either way, this affordable way of studying countermeasure effectiveness will have helped inform decision makers at the City of Toronto on next steps.**