Traffic controllers use standard interfaces that conform to recognized NEMA or ITS standards. Under these standards, the controller uses single function signaling wires to communicate with intersection traffic and pedestrian signals. Modern traffic controllers have far greater capability than are currently utilized because existing interfaces are constrained to one-way communications. Present signal systems are limited as to the type of information, the number of predefined messages that can be displayed or devices controlled.
A model of a Plug-and-Play (PnP) Distributed Signal Network (DSN) traffic controller architecture was demonstrated to selected representatives of FWHA, universities, consultants, and manufacturers of traffic controllers at the TRB Signals Systems committee mid-year meeting in Las Vegas, Nevada (July 10-13, 2005). Attendees at the meeting agreed that existing controller architectures are incapable of providing the fined grained sensing and the degree of control expected to manage today’s transient, automobile, bicycle and pedestrian use of roadways.
The response to our model was overwhelmingly positive, and feedback identified a critical next step in the development of this technology. The system must ensure failsafe operations by including a conflict monitor (CM) before there will be acceptance of this new technology by the state and federal DOT agencies. Since the PnP DSN architecture uses software to a much higher degree to distribute the control information, existing CMs designed for central control hardware-based architectures are no longer able to provide failsafe mode operations. Hence a distributed approach to conflict monitoring is necessary for this technology to move forward.