How Calgary’s Traffic Signals Work

Coordinating Calgary’s traffic signals is a complex balancing act. Here is a look at some of the factors that affect your daily commute.

Photograph by Steve Collins

Traffic signals can feel personal. The fulfillment of light after light switching to green is a high dramatically contrasted by the opposite. As yellow lights appear just beyond reach, commuters can be left cursing the traffic gods.

Of course, the traffic gods are more human than it may seem. Sort of.

Roughly 1,150 traffic signals direct drivers in Calgary. They can be sorted into two camps: coordinated and isolated.

Coordinated lights sync up along Calgary’s 70 established corridors, which range from three to 17 connected sets of lights. In the downtown core, traffic signals are on a pre-timed schedule, changing throughout the day to accommodate rush hours or quieter times on the roads. Nothing pedestrians, cyclists or drivers do impacts these sequences — hence the “audible signal only” pedestrian buttons.

Outside of the core, it’s not that simple. Factors like heavy volumes on side streets, more complicated intersections and pedestrian crossing buttons which do impact light times create a balancing act.

“Overall, the goal is to design (around) the goal of the corridor — how to achieve that coordination, and at what expense,” says Stephen Nicholls, senior traffic engineer in the City of Calgary’s traffic signal engineering group.

This is where detection devices can come in. Both in non-downtown corridors and isolated intersections — that operate independent to other signals — Calgary mainly uses two methods for detecting vehicles: induction loops buried near the stop line, that are interrupted by a metal car stopping above, and cameras that automatically detect cars near the stop line. These devices on side streets, along with a handful of less common methods, help communicate to the light to start cycling.

No system always runs smoothly, however. Disruption of communication between signal controllers — Nicholls describes this as the “brain” of each intersection — can create slight delays. If not remedied quickly, a few seconds here and there can throw the whole corridor off.

While the advanced controllers can often fix themselves, manual solutions are sometimes needed.

In 2020, Calgary began switching over its 22-year-old traffic Central Traffic Control System to TransSuite. By the end of 2021, all signalized intersections will be connected to the centralized system. Along with a larger capacity and ability to connect to newer technologies, the system also allows for by-the-second updates as the controllers connect to their central hub, versus by-the-minute updates on the old system.

“This was mostly a lifecycle replacement. But we also wanted to make sure to get the most advanced system to build that foundation for future technologies,” says Sameer Patil, leader of the Traffic Management Centre (TMC), Calgary’s 24/7 traffic operation hub.

From the TMC, Patil and his team monitor camera feeds at intersections throughout the city, dispatching road crews as needed and communicating to the public through Twitter, radio (107.9 FM) and web updates if something’s gone awry.

Data from the TMC is also shared with other departments, such as Nicholls’ traffic signal engineering group, to help adjust and improve Calgary commutes through adjustments to signals.

Between Nicholls’ 24 years in Calgary traffic and Patil’s 14, the pair have both watched the city’s traffic needs evolve. Bike lanes, for example, added a new variable to the mix — one that Nicholls says is still progressing as new data informs best practices. On crosswalks, recent accommodations like longer walk times where possible and more wheelchair accessibility through ramps and resurfacing has aimed to make Calgary more pedestrian-friendly.

As Calgary’s traffic needs change, Nicholls says the pursuit of making commutes a little less painful is a moving target. That, however, keeps things interesting.

“What I enjoy most about traffic is working to affect solutions that impact a lot of people,” says Nicholls. “Making a difference daily in solving operational challenges and accommodating the needs of people as they change is really, really gratifying.”

Photograph by Steve Collins


Rare Traffic Light Sightings

U-Turn Signals

The first U-turn signals in Alberta are on 17th Avenue S.E. Since the middle lane is now designated as the Bus Rapid Transit route, the signals allow drivers access to businesses on both sides of the avenue.


Transit Left Turn from Right Curb

This signal allows buses to turn left across traffic from the right lane. Look for it at the intersection of Cambrian Drive and Northmount Drive N.W.


Advance Walk Signals

Some crosswalks get a head start before lights turn green to increase visibility of pedestrians. Look for these signals along Edmonton Trail.

Learn more about the people and organizations moving Calgary forward with Avenue's Innovation Newsletter.

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