Distributed Ethernet Network of Advanced Pedestrian Signals

For more than 60 years, traffic signals have used direct wire connections between the traffic controller cabinet and the signals and detectors dispersed throughout the intersection. A network-based approach is reported for distributed control and sensing of traffic signal devices. The motivation of this research has been to improve safety and performance while reducing the cost of a signalized intersection installation. An Ethernet-based network architecture is presented that uses the National Transportation Communications for Intelligent Transportation Systems Protocol (NTCIP) for real-time signal control combined with the IEEE 1588 precision time protocol for robust operation of safety-critical applications synthesized into the term “smart signals.” The investigation focuses on improving accessibility and safety for pedestrians through the use of smart signals. The smart signal paradigm is the basis of an enabling technology that permits complex functioning signals and detectors with self-test capability. The bidirectional communication provides the ability to monitor the operational status of signals and detectors that are currently unobservable by automated traffic controls. The elements of network messaging that enable NTCIP to be used for real-time intersection signal control are presented. The concerns of signal outputs being generated outside the scope of observation for malfunction management units are addressed by implementing a deterministic network. The time performance of the system is evaluated for Simple Network Management Protocol and Simple Transportation Management Protocol network messages. The results of testing on the global network time synchronization are presented and show that inexpensive microprocessors can achieve stable long-term time division multiplexed operation with 100-μs accuracy.