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The King streetcar is moving markedly faster through Toronto’s downtown core after city staff decided to reactivate a technology that raises the chances the transit vehicles will get a green traffic light.

When a pilot project aimed at speeding up the King car began in November, the transponder and sensor system known as transit signal priority (TSP) was turned off as part of an effort to control for variables during the experiment and allow traffic patterns to adjust.

The technology was reactivated at Bathurst Street in April as a trial. But not until early July – eight months into the pilot – was it turned on throughout the area, leading to frustration at the Toronto Transit Commission (TTC) and concern that the experiment wasn’t being allowed to reach its full potential.

Numbers that have not yet been made public by the city show that July was the quickest month for the streetcar since the pilot began. Depending on vehicle direction and time of day, average journey time through the 2.6-kilometre pilot area was between 30 and 126 seconds faster than the previous month, with the biggest improvement being seen eastbound in the evening rush hours.

“[On] the routes in Toronto where there are far more transit riders than drivers, and King is a really great example, it makes sense to do things that will make traffic flow better and get people moving,” said Shelagh Pizey-Allen, head of the advocacy group TTC Riders.

“Before the pilot, you know, King wasn’t working for anyone and I think that transit signal priority is a really key piece to getting transit riders moving and solving congestion.“

City council voted last year to prioritize the streetcar on King Street, the most heavily used surface transit route in Toronto. New rules require motorists to turn at most intersections between Bathurst and Jarvis, restrictions that stop drivers from using the road as a thoroughfare. In the months since, streetcars have moved more quickly and the number of people using them has gone up, while traffic on nearby roads has not been dramatically affected.

However, the improvements came without the benefit of existing technology that would have reduced the vehicles’ chances of getting stopped at a red light.

Trevor Pitman, senior transportation engineer in the TTC’s strategy and service planning department, explains that transit signal priority relies on a transponder on the vehicle sending a signal as it approaches an intersection. If the light is already green, this can prompt it to stay green a bit longer. And if the light is red, this can shorten the time until it turns green again.

The upside for streetcar users is obvious. Mr. Pitman said modelling done years ago showed vehicles would save an average of about eight seconds per intersection. But because some streetcars would naturally encounter a green light anyway, the benefit for the remaining ones would be greater.

However, there are downsides as well. Fiddling with the length of a traffic signal can mess up vehicle flow on the intersecting streets and also reduce the crossing time available for pedestrians. And the effects may be prolonged since it can take a few light cycles to adjust back to the normal timing, only to have another streetcar come along.

Keeping TSP off allowed traffic in the area get accustomed to the new King Street rules and settle into a new pattern that the city could monitor and make tweaks to as necessary.

“Essentially we needed to come up with what would be the optimized signal timing plan for each intersection and TSP is just one component,” said David Kuperman, manager of surface transit projects at the city.

“We started off by developing a baseline, sort of coming up with a signal timing plan that we thought might work for each intersection, and then refining it based on observed traffic patterns, so ensuring that the impacts would be manageable to the overall transportation network. And then, once we had those refined times, we knew we would be able to introduce transit signal priority again.”

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