Traffic signals are electrically operated traffic control
devices which alternately direct traffic to stop and to proceed. This
discussion tells what factors enter into traffic engineers' decisions to
install traffic signals. Because there is a common belief that signals are the
answer to all traffic problems at intersections, this is offered in the
interest of developing broader public understanding about what signals will do
- and what they won't do.
ADVANTAGES
Signals offer the maximum degree of control at intersections
- they relay messages of both what to do and what not to do. The primary
function of any traffic signal is to assign right-of-way to conflicting
movements of traffic at an intersection, and it does this by permitting
conflicting streams of traffic to share the same intersection by means of time
separation.
DISADVANTAGES
While many people realize that traffic signals can reduce
the number of angle collisions at an intersection, few realize that signals can
also cause an increase in other types of accidents (it has been well documented
that other types of accidents, notably rear-end collisions, usually increase
when a signal is installed).
Normally, traffic engineers are willing to trade off an
increase in rear-end collisions for a decrease in the more severe angle
accidents; however, when there is no angle accident problem at an intersection,
there is nothing to trade off and the installation of traffic signals can
actually cause a deterioration in the overall safety at the intersection.
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