The function of a traffic control signal is to alternate and allocate the right-of-way between conflicting streams of vehicular traffic, or vehicular traffic and pedestrians crossing a roadway, with maximum efficiency and safety. Maximum efficiency implies the minimum delay to traffic. Safety requires that the traffic control signals operate at the minimum hazard to vehicles and pedestrians. Traffic control signals, as the name implies are primarily control devices rather than safety devices.
The initiative to consider installing a traffic signal at an existing intersection will generally arise from requests from the public or analysis regarding delay, congestion, safety, or pedestrian crossing problems.
The investigation of the need for a traffic control signal shall begin with the collection of traffic, pedestrian, collision and geometric data. Then, an assessment of whether or not a signal is technically justified is made using the following criteria:
Justification 1 - Minimum Vehicle Volumes
Justification 2 - Delay to Cross Traffic
Justification 3 - Collision Experience
Justification 4 - Combination Justification
Justification 5 - Pedestrian Volume
Unless one or more of the signal justifications are met, the installation of signals would not normally proceed as it would likely result in an increase in overall intersection delay and/or a negative impact on intersection safety.
Unnecessary traffic control signals can lead to excessive delay, increased use of fuel, increased air pollution, increased noise, motorist frustration, greater disobedience of the signals and to the use of alternate routes in attempting to avoid these types of signals.
Unjustified traffic signals may alter the type of collisions and in some cases increase the collision frequency, particularly rear-end collisions, as opposed to right-angle collisions prevalent intersections controlled by stop signs.
Written requests for the installation of traffic control signals should be forwarded to the Transportation Division of the Engineering Department for evaluation.