Will a traffic signal reduce accidents at our intersection?
 UNJUSTIFIED SIGNALS
Traffic signals don't always eliminate collisions. In fact, in most instances, collisions
and severe injuries increase after signals are installed.
The Manual on Uniform Traffic Control Devices suggests that signals should not be installed
under the premise of reducing collisions, unless five or more occur per year. This was
predicated on a comprehensive California study which determined that of all signals installed
over a five year period, the only ones that enjoyed a reduction in collisions were those that
had at least five occurring annually beforehand.
The purpose of signals is to improve the overall flow of traffic. Signals can be helpful in
reducing right-angle collisions under certain circumstances, but almost always increase other
type of collisions such as rear-end and left turn collisions. Unfortunately, signals can also
lull pedestrians into a false sense of security.
WHAT CONDITIONS WARRANT A SIGNAL?
Traffic engineers compare existing conditions against guidelines established after many years
of study throughout the country. If conditions do not meet established guidelines, signalization
will only cause more collisions, congestion and delay. When these conditions are met, an
engineer then needs to consider geometric conditions and spacing to ascertain whether or not a
signal could be helpful.
Signals installed at collector and local street intersections may be necessary to improve
access to major streets, but they can result in more neighborhood cut-through traffic.
Traffic engineers consider these points when deciding if a traffic signal will help more that
it will hurt:
· Is congestion severe enough to create extraordinary frustration?
· Is traffic so heavy that drivers on the side street try to cross when it is unsafe?
· Are there a large number of pedestrians waiting to cross a wide, high speed and busy street?
· Does the age and number of school children crossing the street require special controls?
If so, is a traffic signal the best solution?
· Would a signal allow for a smooth flow of traffic and not adversely affect safety by causing
gridlock with a nearby signal?
Remember, traffic signals
· CAN INCREASE COLLISIONS
· CAN INCREASE NEIGHBORHOOD CUT-THROUGH TRAFFIC
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