Signals

Reasons for Installation


Traffic signals are intended to help move traffic in an orderly fashion. As one of the most restrictive forms of traffic control, signals are installed only where less restrictive signs or markings do not provide enough control. Certain intersections would not be improved or made safer by the installation of a signal.

Unnecessary signals cause annoying delays to drivers and can cause safety concerns. Too many signals increases traffic on side streets as drivers seek alternate routes. Excessive stopping and starting wastes gasoline (and therefore money) and increases carbon monoxide emissions.
Employee Installing Traffic Signs In His Cherry Picker

Accident Reduction


Although it appears that signalization would reduce the number of accidents, studies show this isn't always true. In fact, the potential for rear-end accidents is increased by the installation of a traffic signal.

Criteria for Signal Installation

Traffic engineers ask several standard questions to determine if an intersection needs a signal:
  • Is the volume of traffic at the intersection such that a signal is needed to decrease congestion?
  • Does the intersection have a high volume of pedestrians whose crossing creates significant conflicts with traffic?
  • Do a significant number of drivers on side streets experience excessive delays attempting to cross or enter the major street?
  • Would the number and type of reported accidents be significantly reduced by a signal?

Traffic Studies Provide the Answers


To answer these questions, we conduct traffic studies. We compare traffic volumes and accident history to established industry guidelines for signalization. Analyzing this information determines whether a signal is needed. If an intersection does not meet the criteria for signalization, we look at other alternatives that may improve the intersection.

When a Signal is Needed


Installing a traffic signal typically costs more than $250,000. This cost includes highly specialized control equipment and hardware, underground facilities (detector loops that tell the signal when to change), and engineering and construction of the signal. An intersection that meets our criteria may take several years to be completed as we attempt to secure the necessary funding, usually through state or federal sources.

The county's Transportation Improvement Program lists the intersections that meet signalization criteria and are those locations that we are attempting to fund within the next six years.
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Address:
4301 South Pine Street, Suite 628
Tacoma, WA 98409