Traffic signals don't always
prevent crashes. In fact, in many cases the number of crashes and injuries
increase after signals are installed.
Unnecessary signals can
reduce right-angle collisions, but they can cause an increase in total
crashes, especially rear-end collisions. In addition, pedestrians are often
lulled into a false sense of security.
In deciding whether a traffic signal
will be an asset or a liability, traffic engineers use the following
- Does the number of vehicles on
intersecting streets create confusion or congestion?
- Is traffic on the
main street so heavy that drivers on the side street try to cross when it is
- Does the number of pedestrians attempting to cross a busy main
street create confusion, congestion or hazardous conditions?
- Does the
number of school children crossing a street require special controls for their
protection? If so, is a traffic signal the best solution?
- Will the
installation of a signal allow for continuous, uniform traffic flow with a
minimum number of vehicle stops?
- Does an intersection's crash history
indicate that a signal will reduce accidents?
engineers compare existing conditions with nationally accepted minimum
standards established after many years of studies. Signals generally operate
effectively, that is, with good public compliance, at intersections where
standards have been met.
Where not met, compliance is generally reduced,
resulting in additional hazards. Properly placed traffic signals improve flow
and decrease crashes, while unnecessary signals can create danger and be an
annoyance to pedestrians, cyclists and drivers.
signals are expensive to build, operate and maintain. A typical traffic
signal costs between $200,000 - $350,000 to construct. The annual maintenance cost
for a typical signal is around $3,000. The costs vary by the number of signal
heads and mast arm lengths.