Traffic Signals

Each year, the Public Work's Traffic Division receives inquiries concerning the operation of traffic signals within the County of Shasta. The public's understanding of the function of traffic signals can improve driving habits by reducing speeding and associated traffic accidents. the familiar red, yellow, and green lights are set up to let people know who has the right-of-way at an intersection. Signals help vehicle traffic flow better, allow pedestrians to cross, and give cross-street traffic a chance to cross or enter the intersection.

Why are traffic signals needed?

As traffic volumes increase beyond the capability of lesser controls, such as a four-way stop, it may be necessary to install a traffic signal. Traffic 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 an intersection.

This is done by permitting conflicting streams of traffic to share the same intersection by means of time separation. By alternately assigning right-of-way to various traffic movements, signals provide for the orderly movement of conflicting flows. They may interrupt extremely heavy flows to permit the crossing of minor movements that could not otherwise move safely through an intersection. When installed under conditions that justify the installation of traffic signals, they are valuable devices for improving the safety and efficiency of both pedestrians and vehicular traffic.

How do I get signals on my street?

To install a traffic signal at an intersection, minimum criteria must be reviewed and met:

  • Volume of vehicular and pedestrian traffic
  • Need to provide interruption to the major flow for side street vehicles and pedestrians
  • Accident history of intersection
  • Special conditions, such as hills and curves

How are signals timed?

Traffic signals assign the right-of-way to various traffic movements for different time intervals depending on traffic flow levels. Pre-timed signals have preset time intervals for different times of the day, including the morning, noon, and evening peak travel periods.

Traffic actuated signals use detectors located in the pavement on the approaches to traffic signals to monitor and assign the right-of-way on the basis of changing traffic demand.  These signals attempt to assign most of the available green time to the heaviest traffic movements.  The majority of the County's signals are actuated signals, using detectors. 

Are there any disadvantages to traffic signals?

While many people realize that traffic signals can reduce the number of right angle collisions at an intersection, few realize that signals can also cause a significant increase in rear-end collisions.  In addition to an increase in accident frequency, unjustified traffic signals can also cause excessive delay, disobedience of signals, and diversion of traffic to residential streets.  Traffic signals are not a “cure-all” for traffic problems.  The primary goal of the Traffic Division is to attain the safest and most efficient overall traffic flow possible. 

How much does a traffic signal cost?

Traffic signals are more costly than is commonly realized, even though they represent a sound public investment when justified.  A modern signal can cost approximately $250,000, which includes a traffic signal controller, signal heads, vehicle detectors, and signal poles and supports.

Controller - The controller is the signal's brain.  It consists of electrical or computer controls that operate the selection and timing of traffic movements in accordance with the varying demands of traffic as registered with the controller unit by detectors.

Signal FacesSignal faces are part of a signal head that include solid red, yellow, and green lights and sometimes red, yellow, and green turn arrow lights as well.

Signal Head - A signal head can contain one or more signal faces.

Vehicles Detectors - Vehicle detectors are devices for indicating the passage or presence of vehicles.  In Shasta County, these consist of wire loops placed in the pavement at intersections.  They are activated by the change of electrical inductance caused by a vehicle passing over or standing over the wire loop.