Traffic actuated signals (Vehicle actuated signals)
Actuated signals change the lights according to the amount of traffic in each direction. They use various types of sensors to detect vehicles, and adjust the length of the green time to allow as many vehicles as possible through the intersection before responding to the presence of vehicles on another approach.
Advantages :
- It provides continous operation under low volume conditions.
- Usually reduces delay.
- It is most efficient for isolated intersections.
- Usually increase the capacity.
- It is adaptable to short-term fluctuation in traffic.
Disadvantages :
- Detectors or sensors are very costly to install and present very difficult maintenance problems.
- They are uneconomical. The cost is about two to three times the cost of a fixed time signals.
- The actuated controller (complete electronic mechanism) is much more complicated than fixed time controllers.
Types of traffic actuated signals :
1. Fully actuated signals :
These have detectors located on each approach and assign the right of way to the various traffic movements on the basis of demand.
2. Semi actuated signals :
Where traffic on heavy volume of high speed arteries must be interrupted for relative light class traffic, semi actuated traffic signals are often installed. For these signals the detectors are placed only on the minor street.
3. Speed control signal :
Speed control system is same as fully actuated system, but intersection design based on the major traffic flow will have unpredictable fluctuation.
