Traffic Signals

Department E-mail:

Each year, the City of Eureka receives inquiries concerning the operation of traffic signals within the City. 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.

Q: Why are traffic signals needed?

A: 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.

Q: How do I get signals on my street?

A: 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

The Traffic/Signals Division assigns points in each of these categories and will install traffic signals in the intersections that need them the most.

Q: How are signals timed?

A: Traffic signals assign the right-of-way to various traffic movements for different time intervals depending on traffic flow levels. Pre-timed signals have pre-set 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 City’s signals are actuated signals, using detectors.

Q: What are coordinated traffic signals?

A: The coordination of traffic signals facilitates smooth traffic flow (progressed movement) along a street. The quality of flow along a street is basically a function of the spacing of the signals along the street, the prevailing speed of traffic on the street, and the traffic signal cycle length. The amount of traffic and the proportion of green time given to the progressed movements are also important.

Drivers ask why they have to wait so long for a signal to change. Many of these drivers are waiting to enter a major arterial street from a side street. This is even more frustrating when no traffic can be seen on the arterial. To allow the coordination of the arterial, the side street must wait until the main traffic movement on the arterial has gone through the intersection. It is possible that the arterial traffic cannot be seen immediately, but will soon be passing through the intersection.

The goal of coordination is to get the greatest number of vehicles through the system with the fewest stops, in a comfortable manner. It would be ideal if every vehicle entering the system could proceed through the system without stopping. This is not possible, even in well-spaced, well-defined systems. Therefore, in traffic coordination, the majority rules and the busiest traffic movements are given precedence over the smaller traffic movements.

The greatest benefit to the public for each dollar spent on traffic operations improvements come from the coordination of adjacent traffic signals to provide smooth movement of the traffic through groups of signals on an arterial street. An additional benefit is the elimination of "stop and go traffic," which decreases carbon dioxide emissions, thereby helping to improve the air quality in your area.

Q: Are there any disadvantages to traffic signals?

A: 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/Signals Division is to attain the safest and most efficient overall traffic flow possible.

Q: How do I report a problem at a traffic signal?

A: To report a traffic signal that is not working properly, contact the Traffic/Signal Division at (707) 441-4194. If the problem occurs in the evening or weekends then the report should be made to the Eureka Police Department at (707) 441-4054.


Traffic signals are more costly than is commonly realized, even though they represent a sound public investment when justified. A modern signal can cost up to $200,000, which includes a traffic signal controller, signal heads, vehicle detectors, and signal poles and supports.

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 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. The signal head can contain one or more signal faces.

Detectors are devices for indicating the passage or presence of vehicles. In Eureka, 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.


Flashing Red
According to the California Vehicle Code, when a red lens is illuminated with rapid intermittent red flashes, a driver shall stop before entering the crosswalk on the near side of the intersection. The driver may proceed, subject to the rules applicable to making a stop at a four-way stop controlled intersection.

Dark Signals
When a traffic signal has gone dark, due to power failure, it is considered to function the same way as a four-way controlled intersection. A driver must stop before entering the intersection.



The City is committed to providing the safest, most efficient and advanced Traffic Signal System available. If you have any community traffic concerns, questions, or suggestions, please call the Traffic/Signal Division at (707) 441-4194.



Click below for other Traffic Information:

Children at Play Speed Limits
Crosswalks Stop Signs
Pedestrian Safety Tips Street Lights
Pedestrian Signals Traffic Information Home Page