Traffic Signal System

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The City has two types of traffic signals: fixed-time signals, and traffic actuated signals.

Fixed-time signals are set for average conditions and change at predetermined time intervals.  Traffic actuated signals detect the presence of vehicles, or pedestrians who activate the walk button, and adjust the timing to optimize traffic flow at the intersection.  Traffic actuated signals are used along major arterials and are synchronized to provide coordinated movement.

Signals are installed using various funding sources including: your tax dollars, development fees, and special state and federal grants.  A new traffic signal cost about $85,000 to $175,000 in 2004.

 

Why are traffic signals needed?

 

As traffic volumes increase, it may be necessary to install a traffic signal.  Before installing a traffic signal, the following criteria must be evaluated:

 

  • Amount of vehicular and pedestrian traffic.
  • The need to provide interruption to the major flow for side street vehicles and pedestrians.
  • Accident history of the intersection.

 

Are traffic signals the answer to solving traffic problems?

Advantages of Traffic Signals:  Signals offer maximum control at intersections.  The primary function of any traffic signal is to assign right-of-way to conflicting movements of traffic at the intersection.  By alternately assigning right-of-way to various traffic movements, signals provide for the orderly movement of conflicting flows.  When properly timed, a traffic signal increases the traffic capacity of an intersection.  When installed under conditions that justify its use, a signal is a valuable device for improving the safety and efficiency of both pedestrian and vehicular traffic.  Signals reduce certain types of accidents, most notably right-angle or broadside collisions.

Disadvantages of Traffic Signals:  While many people realize that traffic signals reduce the number of right-angle collisions at an intersection, few realize that signals can also cause an increase in rear-end collisions.  Normal practice includes a willingness to accept an increase in rear-end collisions in exchange for a decrease in more severe, right-angle accidents.  However, when there is no right-angle accident problem and the signal is not needed for traffic control, there is no safety benefit.  In this instance, installation of traffic signals can actually decrease the overall safety at the intersection.

Traffic signals are not a "cure-all" for traffic problems.  In addition to increasing the frequency of rear-end accidents, unjustified traffic signals can also cause excessive delays, and when this occurs, disobedience of signals and diversion of traffic to residential streets.

 

Special signal functions

Emergency Vehicle Pre-emption:  Pre-emption is the transfer of signal control to a special signal operation.  Emergency vehicle pre-emption is used by authorized vehicles — normally fire engines and ambulances.  The purpose of pre-emption is to obtain a green light for the emergency vehicle as soon as possible or to hold an existing green light.

Flashing Red:  A red-flashing light at an intersection alerts a driver to stop before entering the crosswalk.  The driver may then proceed based upon the same rules applicable to making a stop at an intersection controlled by a stop sign.

Flashing Yellow:  A yellow flashing light indicates that a driver may proceed through the intersection with caution.

Flashing Operation:  When volumes are very low, traffic signals can be placed in a flashing operation mode to reduce unnecessary delays.  Englewood has strict criteria that must be met before an intersection will be considered for flashing signal operation.  If the accident rate increases during flashing operation periods, the signal will be changed to regular operation 24 hours per day.

Dark Signals:  A dark traffic signal is considered to function the same way as a four-way stop controlled intersection, and a driver must stop before entering the intersection.

 

Coordination of traffic signals

The greatest public benefit comes from the coordination of adjacent traffic signals to provide smooth movement (progression) of traffic through groups of signals on a major street.  Progressed movement also aids in reducing stops and delays.  Generally, progressed movement on one-way streets or divided highways is readily achieved.  However, providing progression in both directions on two-way streets is much more difficult.

The quality of flow along a street is a function of the spacing of the signals, prevailing speed of traffic, and length of the traffic signal cycle.  The amount of traffic and the proportion of the green time given to progressed movements are also important factors.