Failure Analysis of Network Based Accessible Pedestrian Signals in Closed-Loop Operation

摘要

The potential failure modes of a network based accessible pedestrian system were analyzed to determine the limitations and benefits of closed-loop operation. The vulnerabilities of the system are accessed using the industry standard process know as Failure Modes and Effects Analysis. This analysis reveals that because the closed-looped operation increases operational observability, there is only one failure mode that is not detectible. Investigation on reliability of hardware and software indicate that the probability of this particular event is extremely low. The three primary components of a distributed real-time control system are hardware, software, and communications. Environmental conditions are the predominant factors that determine hardware reliability. The system was tested for its ability to function in the presence of electrical transients specified by the National Electrical Manufacturers Association (NEMA). All hardware components meet or exceed NEMA temperature requirements. Software errors are difficult to detect and difficult to predict. Best practices in development and testing can minimize the number of errors. Testing includes multiple years of both laboratory and field testing.