Traffic Signal FAQs

What does a traffic signal do?
What should I do at dark signals?
Do traffic signals control speeding?
Do traffic signals reduce collisions?
Who should I call if a signal is out or pole has been knocked over?
What is Traffic Signal Preemption?
Why aren't the signals timed so I never have to stop?
Why do I have to wait when there's no one coming?
Why don't I always get a left-turn arrow?
What are Fully Protected Left-turn Signals
What are Protected/Permissive Left-turn Signals
 

Q: What does a traffic signal do?
A: Traffic signals guide drivers and pedestrians through intersections and along roads. They tell road users when to stop and go, when and how to turn and when to drive with extra caution.

Q: What should I do at dark signals?
A:  During an electrical power loss, traffic lights at intersections will not work. Yield the right-of-way to vehicles in the intersection and to vehicles entering the intersection from your right. Go cautiously and use the intersection the same way you would use an intersection with all-way stop signs.

Q: Do traffic signals control speeding?
A:  No. Traffic signals may actually result in higher speeds if drivers accelerate to get through an intersection before the signal turns red. Traffic signals are not intended to be used as a traffic calming measure.

Q: Do traffic signals reduce collisions?
A:  Traffic signals may reduce the number of angle collisions; however, they can also increase other types of collisions such as rear-end collisions. The decrease in the more severe angle collisions is weighed against the likelihood of an increase in the number of the generally less severe rear-end collisions. If there is no history of angle collisions then traffic signals may increase the collision rate at an intersection.

Q: Who should I call if a signal is out or pole has been knocked over?
A:  To report traffic signal outages and knockdowns please call 519 661-2641 and press 2 when prompted. This will connect you directly to the City’s traffic signal maintenance contractor.

Q: What is Traffic Signal Preemption?
A:  The transfer of signal control to a special signal operation is called preemption. In London, all fire vehicles are equipped with preemption equipment and some railway crossings are also equipped with preemption equipment.

Railroad preemption is initiated when a train passes over advance detectors located on the tracks. The purpose of preemption is to clear tracks of traffic stopped on them by traffic signals.

Fire vehicle preemption gives a green light for the fire vehicle as soon as possible or it may hold an existing green light. To obtain a green light, existing green lights, are abbreviated.

Q: Why aren't the signals timed so I never have to stop?
A:  Traffic signals cannot give everyone a green light or walk signal all the time. Traffic signals are timed to move the most number of vehicles through an intersection and along a corridor in the most safe and efficient manner. This may result in longer delays for side street traffic; however, the overall delay at an intersection is reduced.

There are also many other factors that impact the operation of the traffic signals. Closely spaced signals, intersections where major streets cross, changing traffic volumes and weather all add to the difficulty of minimizing stop and go traffic for all directions of travel. Fire trucks have the ability to change the signal to green or hold the green. This disrupts the timing patterns at intersections for as much as 10 minutes; therefore, the signals are impacted well after the fire vehicle has left the intersection.

Q: Why do I have to wait when there's no one coming?
A:  Many drivers ask why they have to wait so long for a signal to change. Many of these drivers are waiting to enter a major arterial street from a side street. This is even more frustrating when no traffic can be seen on the arterial. To allow the coordination of the arterial, the side street must wait until the main traffic movement on the arterial has gone through the intersection. It is possible that the arterial traffic can’t be seen immediately, but will soon be passing through the intersection.

Some signals, particularly in the downtown, don't have the necessary equipment to detect when cars are approaching. At other intersections the vehicle detection or pedestrian push button equipment may have failed. For both of these cases the traffic signal will cycle to the side street regardless if there are vehicles or pedestrians present.

Pedestrian crossing times (Walk and Don't Walk) may require longer green intervals than the vehicles; therefore, the traffic signal may stay green when no vehicles are present.

The impact of a fire truck on a traffic signal may be experienced even after the fire vehicle is out of sight.

Q: Why don't I always get a left-turn arrow?
A:  Left-turn arrows are great if you're the one turning left, however, they generally make the wait longer for everyone else at the intersection. Traffic engineers balance the benefit of adding a left-turn arrow for the minor vehicle movement (left-turners) against the overall delay for the other more major movements.

Left-turn arrows are sometimes turned off during lower volume times of day when the turns can be made through existing gaps or may be displayed only when there are sufficient numbers of vehicles waiting in the left-turn lane to warrant the left-turn signal.

Left-turn arrows are a definite convenience for the lower volume left-turning traffic, but since the allotted time for the arrow must be taken away from the much heavier opposing through traffic, overall intersection delay is increased.

Q: What are Fully Protected Left-turn Signals
A:  With this type of left-turn signal, separate signal heads display a green arrow followed by an amber arrow, and then a solid red display. On the green arrow, drivers are given the right-of-way to turn left only. The amber arrow warns drivers that the left-turn signal is ending. Left-turn movements are not permitted during the through green displays.

Fully protected left-turn signals may be implemented at dual-left-turn lanes or to address high incidences of left-turn collisions.

Q: What are Protected/Permissive Left-turn Signals
A:  Protected/Permissive left-turn signals will display a green left-turn arrow allowing for a protected left-turn movement, often followed by a yellow left-turn arrow indicating that the protected left-turn is ending. A green permissive ball is then displayed which allows waiting left-turn vehicles to proceed with the left-turn during acceptable safe gaps in the opposing through traffic.