C-DAC Thiruvananthapuram has developed a Wireless Traffic Signal Controller (Wi-TraC) with distinct advantages over conventional traffic signal controllers. The impetus for developing the Wi-TraC has been the increasing problems with conventional controllers. Due to the tremendous increase in vehicles, number of roads and the number of road intersections, the need for traffic controllers is increasing every day. But installing conventional, wired traffic controllers is difficult for the agencies involved.
The traditional way of installing conventional traffic controllers is to mount the controller box on a 2’x 2’x 3’ pedestal on the pavement. This normally obstructs pedestrian movement. Further, in a conventional traffic controller all the signal lamps or poles are physically linked to the control electronics through copper cables. This requires digging one-foot wide and one-and-a-half foot deep ducts across the road from the traffic controller equipment to the signal poles, installing Hume pipes in the ducts and pulling multi-core armoured cable through the pipes. Often, this process damages good roads, seriously affecting their life span. Disturbance to road users, both drivers and pedestrians, and possibility of damaging other utilities such as telephone cables, electric cables and water lines are other hazards. Added to this is the fact that digging of roads during monsoon is often very difficult, if not impossible. Acquiring permissions from various local authorities for digging the roads is another hurdle. A principal reason for the high cost of installing conventional traffic signal controllers is the extensive digging and cable work required.
The Wi-TraC wireless traffic controller, developed with funding from Department of Technology (DIT), eliminates most of these problems. It is an Area Traffic Control System (ATCS) compatible Vehicle Actuated (VA) road traffic signal controller, the most sophisticated of its class. It has many advantages over conventional traffic controllers in terms of functional features, energy efficiency and size. Since it is small and pole mountable, it does not occupy any space on the pavement. It is in fact a cost effective solution for all the issues listed above – no digging, no Hume pipes and no armoured cables. The Wi-TraC is designed to operate on solar power. It has GPS enabled Real-time Clock (RTC) for distributed time synchronisation. The result is easy installation, high availability (no cable faults or RTC corruption) and less cost of installation.
The Wi-TraC is a 32-bit microcontroller-based intelligent road traffic controller with a distributed architecture. It consists of a master controller and a number of slave controllers. The traffic junction plan resides in the master controller. Every island or signal pole has a slave controller. The signal lamps are driven from the master controller and the slave controller of the respective signal poles. The number of slave controllers required depends on the junction geometry, e.g. for a four-arm traffic intersection, one master controller and three slave controllers will be required. The Wi-TraC can support up to 16 slave controllers. The master-slave communication is done on the 2.4 GHz license-free band. In situations where signals are jammed on the 2.4GHz band, the Wi-TraC automatically switches to the backup frequency of 868MHz that is also license-free.
For switching the signal lamps, the master controller establishes communication link with the slave controllers by sending wireless ping commands. An acknowledgement received from the slave controller indicates that the link has been established. The master controller then sends information of the lamp outputs to the slave controller whenever a stage change occurs. The slave controller decodes the logic and switches on the lamp as per the pattern of commands received. In case of dropped packets, the master controller retransmits the commands. When the master controller fails, all slaves go into Flashing Yellow mode after a preset time-out period. In case of failure of any slave controller, all other slaves and the master go into Flashing Yellow mode and this information is logged locally as well as sent to the remote server (if linked to the traffic monitoring centre) for taking action. All packets of communication are encrypted by 128 bit AES (Advanced Encryption Standard).
The Wi-TraC user interface contains a 20×4 LCD display and a 5×4 keypad. Traffic plan data is entered through the user interface or with a laptop or, if networked to the traffic monitoring centre, downloaded from the remote computer. Wi-TraC has 16 optically isolated vehicle detector interfaces compatible with both inductive loop detection and camera based virtual loop detection – the most common methods of vehicle detection. The GPS enabled RTC ensures accurate real-time clock to synchronise with the adjacent intersection controller. Police personnel can use the wireless police panel interface to put the traffic lights at the intersection in flash mode, manual mode and hurry call mode or they can even turn off the lights with a hand-held remote control. The Wi-TraC supports PC interface for reading and writing plans and configurations. It is also possible to do the plan editing remotely from the ATCS.
The Wi-TraC consumes significantly less power than solar powered conventional traffic controllers too because it operates on 12V DC whereas conventional controllers operate on 24V DC. The size of the Wi-TraC panel is also much smaller as a consequence. Another important feature of the Wi-TraC is its ability to control intensity of the signal lamps through Pulse Width Modulation (PWM). Luminosity designed for daytime, operation of signal lamps can be quite disturbing for motorists during night. But with the Wi-TraC, the intensity of the signal lamps can be decreased during night as they can be programmed to operate with different signal intensities depending on the ambient light. This also helps in saving a significant amount of power. Moreover, since Wi-TraC does not use armoured cable for interconnecting the master controller and the signal heads, an average saving of 30% to 40% in civil work, and laying of cables, pipes and conduits has been envisaged compared to the conventional traffic signal installation.