Traffic Signals

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Traffic Signals

The Capital Projects and Transportation Department operates and maintains all traffic signals in the City. Traffic Signals are valuable devices for the control of vehicle and pedestrian traffic. The public's understanding of the function of traffic signals can improve driving habits by slowing traffic and reducing traffic collisions. The more drivers that understand how traffic signals work, the less they will be frustrated when waiting for a signal to change.


Malfunctioning Traffic Signal?

Please have the intersection locations available when reporting the traffic signal malfunction. You can report the malfunction my visiting the office, email, or by phone. For the fastest response, please call or visit the office. 

City of West Sacramento

1110 West Capitol Avenue

West Sacramento, CA 95691

Phone Number: (916) 617-4720

Email Address:

Are Traffic Signals the Answer to Solving Traffic Problems?


Signals offer maximum control at intersections--they relay messages to both what to do and what not to do. By alternately assigning right-of-way to various traffic movements, signals provide for the orderly movement of conflicting vehicles and pedestrians. They may interrupt the main street which carries extremely heavy flows to allow the minor street movements that could not otherwise move safely through an intersection. When traffic signals are properly timed, they increase the traffic handling capacity of an intersection and when installed under appropriate conditions a signal will improve efficiency and the safety for both vehicles and pedestrians. In particular, signals can reduce the frequency of certain types of collisions, especially right-angle (broadside) collisions.


Traffic signals are not a "cure-all" for traffic problems. Even though warranted by the traffic and roadway conditions, poor design, bad placement, improper operation, or poor maintenance can make them ineffective. While many people realize traffic signals can reduce right-angle collisions at an intersection, few realize that signals can also cause a significant increase in rear-end collisions. When there is no collision problem at an intersection and a signal is not needed for traffic control, there is no benefit to the installation of traffic signals. In fact, they can cause a reduction in the overall safety at the intersection. Unjustified signals can also cause excessive delay, disobedience of signals, and the diversion of traffic to residential streets.

Special Signal Functions

Traffic Signal Preemption

The transfer of normal traffic signal operation to a special operation is called preemption. There are three common types if preemption: Railroad Train, Emergency Vehicle, or Bus/Transit Vehicles.

Railroad Preemption

Railroad preemptions happen when a train passes over detectors located on the tracks ahead of the railroad crossing. The purpose of the preemption is to clear tracks of traffic stopped on them by traffic signals.

Emergency Vehicle Preemption

In the City of West Sacramento, fire engines are the only emergency vehicle to use preemption. The purpose is to shorten response time by turning on a green light for the fire engine as soon as possible or holding an existing green light. In order for a fire engine to obtain a green light, existing green lights, including the pedestrian interval, are shortened. The fire truck uses a strobe light to trigger a detector that is mounted on the signal.

Bus/Transit Vehicle Preemption

The bus/transit vehicle preemption system is not used in the City of West Sacramento.

Signal Timing

Goal of Signal Timing

The goal of signal timing and coordination is to get the greatest number of vehicles through a particular corridor and to improve the flow of traffic along a major street or through a network of streets.

Traffic signals assign the right-of-way to various traffic movements. The signals have preset time intervals for different times of the day, including morning, noon, and evening peak travel periods. Timing plans are normally selected by a time clock. If a signal should get out of step, the system automatically corrects itself. The local controller for one intersection acts as the master controller for the system.

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 give most of the available green time to the heaviest traffic movements. The cost of an actuated signal is much greater than the cost of a pre-timed signal.

Actuated vs. Fixed Time Signal Control

Traffic signals are programmed to produce the best flow of traffic for each individual intersection. Furthermore, there are different methods in which traffic signals are programmed to run. For example, signals can be timed to operate on an actuated or a fixed time signal control. A fixed-timed signal, or pre-timed control, is a consistent and regularly repeated sequence of signal indications that is given to traffic.

On the other hand, semi-actuated or full-actuated timed signals occur when the duration of some or all of the intervals vary from cycle to cycle; or some phases may be omitted altogether during a cycle. The duration of some or all of the intervals and whether a phase is served or omitted is determined based on actuation from detection equipment.

Coordinated vs. Independent Traffic Signal Operations

In addition to timing an individual traffic signal, some signals are also timed as coordinated in order to achieve a total network of unified traffic signals. This is a predetermined timing relationship among adjacent signals. The goals of coordinating the signals are to minimize delay, minimize stops, and to progress the flow of traffic.

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