FACTORS AFFECTING DESIGN OF TRAFFIC SIGNALS
The IRC method for designing traffic signs implies the following factors affect the design of traffic signals
- Cycle: A signal cycle is one complete rotation through all of the indications provided
- Cycle length: Cycle length is the time in seconds that it takes a signal to complete one full cycle of indications. It indicates the time interval between the starting of of green for one approach till the next time the green starts. It is denoted by C.
- Interval: Thus it indicates the change from one stage to another. There are two types of intervals -
- change interval and
- clearance interval.
- Change interval is also called the yellow time indicates the interval between the green and red signal indications for an approach.
- Clearance interval is also called all red is included after each yellow interval indicating a period during which all signal faces show red and is used for clearing off the vehicles in the intersection.
- Green interval: It is the green indication for a particular movement or set of movements and is denoted by Gi. This is the actual duration the green light of a traffic signal is lit.
- Red interval: It is the red indication for a particular movement or set of movements and is denoted by Ri. This is the actual duration the red light of a traffic signal is lit.
- Phase: A phase is the green interval plus the change and clearance intervals that follow it. Thus, during green interval, non conflicting movements are assigned into each phase. It allows a set of movements to flow and safely halt the flow before the phase of another set of movements start.
- Lost time: It indicates the time during which the intersection is not effectively utilized for any movement. For example, when the signal for an approach turns from red to green, the driver of the vehicle which is in the front of the queue, will take some time to perceive the signal (usually called as reaction time) and some time will be lost here before he moves.
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