There are four different traffic signal types:
- Uncoordinated Fixed Time Signals: These traffic signals are observed in rural areas that do not have traffic signals in close proximity and thereby do not require coordination. The signal timings in these signals are pre-timed to suit the existing traffic demand. Timely revisions to signal timing plans will be performed when congestion is identified.
- Uncoordinated Traffic Actuated Signals: These traffic signals are usually observed at a major and minor street intersections. In-pavement loop detectors are installed to detect the minor street traffic and thereby activate the minor street signal timing. These signals are beneficial in intersections with minimum minor street traffic, as major street traffic is not disturbed unless a minor street demand is observed.
- Coordinated Progressive Signals: These traffic signals can be observed in urban areas with busy traffic conditions. Several intersection signals will be operated through coordination and hence a constant flow of traffic is maintained.
- Coordinated Traffic Adaptive Signals: These traffic signals are observed in streets with unpredictable traffic demand shifts. Actuated signals will identify the approaches with peak demand and adjust the signal timings accordingly. In addition, coordination of signals will help in active and dynamic management of traffic demand.
Criteria for selecting signal type: In general, pre-timed control signals are less expensive to install and maintain.Uncoordinated traffic signals are most suitable for intersections with simple and predictable traffic movements on all approaches. However, in areas with complex and unpredictable traffic conditions, actuated signals are proven to be more beneficial. Further, actuated signals have the flexibility of operating fully actuated, semi actuated, or pre-timed. The operation type may also change by time of day.Coordinated and pre-timed signal types have proven to be more efficient than actuated signals. The pre-timed signals ensure consistent starting time and duration of intervals.This capability permits progressive traffic movements and maximizes efficiency.