Traffic Signal FAQs
On this page you'll find answers to the
following Frequently Asked Questions (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
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 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