Traffic Signals


Traffic signals

We receive many enquiries concerning the operation of traffic signals.  A clearer understanding of how traffic signals work can improve driving and walking habits, and reduce some of your frustration while waiting for a signal to change.

Why are Traffic Signals needed?

When traffic volumes increase beyond the capacity of an all-way stop sign, it may be necessary to install a traffic signal.  The established criteria for installing traffic signals is based on the total vehicle and pedestrian volumes, delays to side street motorists and pedestrians, and collision history at the intersection.

Are Traffic Signals the answer to solving traffic problems?

The function of a traffic signal is to assign right-of-way between two or more flows of traffic at an intersection.  A properly timed traffic signal can significantly increase the traffic through an intersection and can improve the safety for both pedestrians and vehicles.

Disadvantages of Traffic Signals

Traffic signals are not a "cure-all” for traffic problems, nor will they prevent collisions.  Unjustified traffic signals can cause excessive delays, a disregard for the traffic laws, diversion of traffic through residential neighbourhoods, as well as an increase in collisions.

A traffic signal is a control device, not a safety device.  While many people realize that traffic signals can reduce the number of right-angle (broadside) collisions at intersections, few realize that signals can also cause a significant increase in rear-end collisions.

Traffic Signal Equipment

Traffic signals are more costly than commonly realized, even though they are a sound public investment when justified.  A new signal costs approximately $150,000 to $200,000.  The equipment is highly specialized and expensive to install and maintain, therefore, the decision to install signals must be carefully considered.

Left Turn Phasing

special left turn phase

It is sometimes necessary to install protective left turn phasing at locations with high volumes of left turning vehicles, where there is excessive delay, or where turning movement collisions are common.

Flashing Red

The rules of the road in the Highway Traffic Act require motorists to stop before entering a signalized intersection when they see a flashing red signal.  You must stop at the white stop bar or crosswalk, on the near side of the intersection.  You should treat a flashing red traffic signal like you would a stop sign, and enter the intersection only if the way is clear.

You may also see a flashing red light or a red beacon at a stop sign or at a multi-way stop.  The red flashing signal is to supplement the stop sign.  At these intersections, enter only if the way is clear.

Flashing Yellow

When traffic signals are flashing amber, it means that the other approach has a flashing red display and motorists may proceed through the intersection with caution.

Signals Out


When there is no power at a traffic signal and all the lights are dark, you should treat the intersection as if it were an all-way stop.  Enter the intersection, subject to the rules at an all-way stop.

Traffic Signal Preemption

Trains and some fire trucks are given priority at traffic signals.  When they approach an intersection, the signals transfer control to a special signal operation called preemption.  In preemption, the traffic controller safely provides a green signal for the approaching emergency vehicle, or prevents vehicles from crossing the railway tracks.

Signal Timing

Traffic signals are timed to alternate right-of-way between two or more approaches.  Traffic signals may be programmed to operate with fixed timing.  However, at many intersections, vehicle detectors are used to assign the right-of-way and signal timing at an intersection will vary, based on changing traffic demands.  The majority of our vehicle detectors are loops of wire imbedded in the pavement and when sensing the metal in cars, signal to the traffic controller, the presence of vehicles.  The City also uses video and thermal cameras to detect the presence of vehicles.

Coordination of Traffic Signals

Coordination of traffic signals provides the greatest benefit to motorists by reducing interruption in the flow of traffic.  Co-ordination along a street is based on signal spacing the volume and speed of traffic, and the traffic signal cycle length.  A well managed coordinated traffic control system saves fuel, reduces travel time, and reduces air-borne pollutants.

The goal of coordinating traffic signals is to get the greatest number of vehicles through the signal network with the fewest stops and delays, in a safe and comfortable manner.  Where optimum conditions cannot be achieved, the intersection approaches with the busiest traffic movement are given priority.

Almost all the City's traffic signals along major arterials are interconnected and operate co-ordinated.


Why do traffic signals on the side street change so quickly?

Many traffic signals operate in a semi-actuated mode where the green times are assigned to the side street, based on the traffic volume from the side street.  If all the vehicles waiting at the intersection clear before the maximum green time is reached, the green signal will change to amber.  This provides more green time for the main street which makes the overall operation more efficient.

Why do I have to wait so long for the signal to change?

At actuated traffic signals, the green phase for the side street will only occur with the detection of a vehicle or someone pushing a pedestrian push button.  The length of delay before getting a green will depend on when the call for a green on the side street was received and if the main street traffic has been satisfied.  In a coordinated system, the call may be further held up to maintain the main street progression.  In these instances, the side street movement can only be serviced after the main street traffic stream has passed through the intersection.  It can be frustrating when there is no traffic on the major street and you must wait.

How are the pedestrian crossing times calculated?

The time for pedestrian "Walk” and  "Flashing Don't Walk” intervals is based on the distance across the intersection that a pedestrian follows.  We calculate the pedestrian crossing time based on the average pedestrian walking speed and the roadway width.  At locations where there are a lot of seniors or children, a slower walking speed is used to lengthen the pedestrian "Flashing Don't Walk” intervals.

Does somebody have to be hurt before a traffic signal will be installed?

Traffic signals don't always prevent collisions and don't always help traffic control.  At some locations, collisions actually increased after signals were installed.   The potential for pedestrian / vehicle conflict may also increases since some motorists do not always recognize the rights of pedestrians at a crosswalk.  Where traffic signals are installed without justification, motorists see them as unnecessary, resulting in non-compliance to traffic laws.  When this happens, traffic signals become a liability to safety rather than an asset.

Why don't all traffic signals have left turn phasing?

There are proper applications for left turn phases.  They should not be over used or implemented at signals that can function effectively and safely without protecting left turns.  The requirement for left turn phasing depends on vehicle volume, number of left turns, delay, collisions and intersection geometry.  The implementation of left turn phasing reduces the amount of green time available for all other movements.  In some instances, left turn phasing results in the interruption of the progressive traffic flow within a coordinated system.