As vehicle volumes increase beyond the capability of sign-based control such as stop signs, it may be necessary to install a traffic signal.  The primary function of any traffic signal is to assign right-of-way to conflicting movements of traffic at an intersection by permitting conflicting streams of traffic to share the same intersection by means of time separation.  New technology such as video detection and signal coordination can be implemented to improve efficiency and increase levels of service.

Traffic signals

By alternately assigning the right-of-way to various traffic movements, traffic signals provide for the orderly movement of conflicting flows. They may interrupt heavy traffic flows to permit minor movements to cross the intersection that could not otherwise do so safely. When properly timed, a traffic signal increases the traffic capacity of an intersection, and when installed under conditions that justify its use, a traffic signal can improve safety and maximize efficiency of pedestrian and vehicular traffic.

While many people realize that traffic signals can reduce the number of right-angle collisions at an intersections, few realize that traffic signals can cause an increase in other types of accidents, most notably, rear-end collisions. Traffic signals are not a cure-all for traffic problems and their implementation must be carefully analyzed.

The criteria that the city uses to determine whether or not a traffic signal is justified at a particular location is based on the Traffic Signal Warrants found in the California MUTCD. The biannual Traffic Signal Evaluation Policy includes a Traffic Signal Qualification List to help identify and compare non-signalized intersections that may benefit from signalization.

The greatest benefit to the public provided by traffic signals comes from the coordination of adjacent traffic signals.  Coordination maximizes the efficiency of traffic movement through groups of signals.  The quality of flow along any given street is a function of the distance between adjacent traffic signals, the prevailing traffic speeds and the traffic signal cycle length.

The goal of coordination is allow the greatest number of vehicles through the corridor while minimizing the stops.  In ideal conditions, a vehicle entering the corridor on one end could travel the entire length without stopping.  Maximizing the efficiency of travel along the major corridors comes at the expense of increased delays on the side streets.  Typically, drivers may have to wait 1-2 minutes for a green light on a side street.  During the morning and evening weekday commutes, the wait on the side street may be as long as 3 minutes.

The Traffic Division is currently evaluating the need to tie the city's traffic signal system into a communication network that will allow real-time monitoring of traffic signal system.  Such a system would allow staff to implement timely adjustments to traffic signal timing plans to account for incidents and daily changes to traffic patterns.

Proper signing and striping is essential in providing drivers with the information necessary to negotiate the city's roadways safely and efficiently. The city utilizes the standards and guidelines found in the California Manual on Uniform Traffic Control Devices (MUTCD).

Construction in the city can inconvenience residents and travelers. The Traffic Division reviews traffic control plans to balance the safety of construction workers with the need to minimize delays for drivers.