Each year, the City receives many inquiries concerning the operation of traffic signals. The public’s understanding of the function of traffic signals can improve driving habits by reducing speeding, traffic accidents, fuel consumption and air pollution. The more drivers know about the operation of traffic signals, the less they will be frustrated when waiting for a signal to change.
Select a topic to learn more:
Installation Criteria, Advantages, Disadvantages, and Cost
Before installing a traffic signal, the following criteria must be evaluated:
- The amount of vehicular and pedestrian traffic
- The need to provide interruption to the major flow for side street vehicles and pedestrians
- Special conditions such as hills and curves
- The accident history of the intersection
- The proximity of schools
Advantage of Signals
- Signals establish right-of-way
- Reduce right-angle accidents
- Provide adequate time for pedestrians and vehicles to cross the intersection
Disadvantages of Signals
- Increase rear-end accidents
- Can cause excessive delay
- Disobedience of signals
- Diversion of traffic to residential streets.
- Traffic Signal Equipment
Costs of Signals
Traffic signals are more costly than is commonly realized. A modern signal can cost around $150,000. This pays for:
- A traffic signal controller - the signal’s brain
- Signal heads - red, green and yellow lights, etc.
- Vehicle detectors - wire loops or video cameras that detect cars
- Signal poles and supports
- Other signal hardware
The length of green time allocated for each movement depends on the amount of traffic. Heavier movements receive more green time.
Traffic actuated signals use detectors located in the pavement or above ground on the approaches to traffic signals to monitor and assign the right-of-way based on changing traffic demand. These signals attempt to assign most of the available green time to the heaviest traffic movements.
Coordination of Traffic Signals:
The City’s traffic signals are supervised by a master computer. City staff uses this computer to coordinate the traffic signals on major streets throughout the day.
The goal of coordination is to get the greatest number of vehicles through the system with the fewest stops. Heavier traffic movements are given precedence over lighter traffic movements. The traffic signal master assigns different cycle lengths to the signals during the day. The length is determined by traffic demand.
City traffic engineers and technicians are constantly upgrading the City’s system by monitoring traffic volumes on street and turning movements at busy intersections. This information is used to time the signals and help traffic flow with less delay. How well traffic flows along a street depends on several factors:
- The spacing of the signals along the street
- Signal timing
- Traffic volume
- Number of traffic lanes and their availability
- Driver behavior and speed
- Physical characteristics of the roadway
Many drivers ask why they have to wait so long for a signal to change. 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 can’t be seen immediately, but will soon be passing through the intersection.