TrafficInfraTech Magazine Linking People Places & Progress
Modes of Operation
The Wi-TraC supports the following modes of operation
Fixed: The input signals from the vehicle detection system are ignored in this mode. The controller will operate with fixed time periods from the timetable. The controller always starts from Stage 1 on restart.
Vehicle Actuated: The Vehicle Actuated strategy allocates green time to a running phase within the constraints of a fixed minimum and maximum green time setting for the phase. This depends on the real-time demand reported by the vehicle detectors. With fully actuated control, all signal phases are actuated and all signalised movements require detection.
ATCS: The controller will execute the signal timing proposed by the ATCS server.
Coordinated (Cable-less): The Cable-less Linking Facility allows a method of coordinating traffic signals along a route and/or in an area using timing information. The Distributed Time Synchronisation (DTS) is achieved by GPS enabled Real-time Clock in the controller.
Manual: Manual operation of the traffic signal stage sequence is required to cater to situations such as abnormal congestion, accidents, breakdowns and other special occasions. In Manual mode the stages appear in the order specified in the timetable with time periods defined by the person manning the junction.
Hurry Call: The purpose of Hurry Call is to give prioritised right of way to certain vehicles on demand. A maximum of four hurry calls can be predefined in the system, and are activated through switches on the police control panel.
Flash Mode: In the Flash mode, selected lamps are made to flash. The lamps can be amber, red or a combination of both. This mode can be selected either through timetable or by control switch.
Signal Plans
The Wi-TraC supports various signal plans as listed below:
32 – Phase Plan: A Phase is a right-of-way signal that is defined by one, two or three signal lights.
The Vehicle phase contains three signal aspects, viz. red, amber and green. The termination of vehicle phase is always with amber. The sequence of signal switching is red-green-amber-red. The Pedestrian phase contains two signal aspects, viz. red and green. The termination of pedestrian phase can be either red flash or green flash. The sequence of signal switching is red-green-red flash or green flash-red.
The Filter green phase provides signal for the right turning traffic. When linked with a vehicle phase the termination of filter green is blackout. Otherwise, it flashes for a few seconds before termination. The Indicative green phase is a continuously flashing signal which provides signal for the left turning traffic. The termination of indicative green is always blackout.
Dummy Phase is a filter to manage the lane change at the detection zone in Vehicle Actuated mode of signal operation. This is not associated with any signal lamp but the signal timing is based on the detection input to the Dummy phase.
32 – Stage Plan: A stage can primarily be considered as a condition of traffic lights during a period of the cycle, which gives right-of-way to one or more traffic movements.
24 – Cycle Plan: Cycle is a scheme in which stages are given some fixed order.
20 – Day Plan: Day Plan is the distribution of cycle plans for a particular day.
4 – Week Plan: Week Plan is the distribution of available day plans for a week.
20 – Special Day plan: Holidays falling on normal weekdays can be treated as special days and can have a different day plan, selected from the available day plans.
All Red Plan: A condition when only red aspects are displayed. The All Red is executed when an abrupt signal change is required (e.g. power up, flash-to-signal, manual-to-auto, hurry call-to-auto, etc). This is a programmable interval from 0 to 5 seconds.
Conflict Plan: Any two phases that are not allowed simultaneously are defined as conflicting phases. The Conflict plan is a listing of all conflicting groups. The system supports listing of all possible conflicting phases. A conflict detected either at the plan time or on hardware failure will force the signals into Flashing Amber.
Start Amber Plan: The Start Amber is a programmable interval for a period of five to 10 seconds. The Start Amber executes the Flashing signal for the programmed interval followed by All Red when the Wi-TraC powers up.
Red Extension Plan: When a right-of-way is terminated, opening of the next right-of-way is delayed by a time period called Red Extension. With no continuing phase, this gives an effect of all red between stage changes. The Red Extension gives an additional clearance time after the Amber. The Red Extension is a programmable period of zero to five seconds.
The Wi-TraC keeps an error log and reports error like lamp failure, output short circuit, green-green conflict, detector failure, communication failure and power failure. Both Master and Slave controllers are pole mountable in IP65 compliant cabinet. The system provides easy access to the user interface and control electronics for enhanced serviceability. Provision to house vehicle detectors inside the cabinet is also available.
The trial results have been favourable and satisfactory for using Wi-TraC in 24×7 operations. C-DAC also plans to install Wi-TraC at Pune in the near future.
P Ravikumar
Joint Director, CDAC
Thiruvananthapuram
R Prakash
Senior Engineer, CDAC
Thiruvananthapuram
(The authors wish to acknowledge the valuable help received from the Department of Information Technology, Ministry of Communications & Information Technology, Govt. of India, Traffic Signals Division, KELTRON, Trivandrum and Thiruvananthapuram Road Development Company Limited (TRDCL) in the development of Wi-TraC).