A balancing act: the superior performance and reliability of microprocessor -based transit vehicle systems trumps older technology, hands down. But standardization and interoperability still have a long way to go:
Chief mechanical officers have a love-hate relationship with microprocessor-driven vehicle systems. While the technology helps commuter, rapid transit, and LRT cars operate more efficiently--offering improved reliability, maintainability, and features--its complexity can send maintainers to the nearest medicine cabinet for aspirin.
"Back in the early 80s, we used to say that microprocessors were a solution waiting for a problem," says Jim Dietz, IEEE Rail Transit Vehicle Interface Standards Committee chair and senior consultant for LTK Engineering Services. "They were a great new thing that everybody wanted to have, but no one was quite sure what to do with them. They've come a long way since then."
Today, microprocessors are ubiquitous. Because of their solid performance record, they are used in control, diagnostics, and monitoring and communications systems. Many new applications, like a.c. propulsion, would be impossible without them.
"Railcar safety and operational integrity used to be defined by contact closures, relays, and switches," says Lou Sanders, director of research and technology at the American Public Transportation Association. "You could see how they worked, and they were designed such that if a relay dropped out, for example, it reverted to a state that was known to be safe. Now, we're taking that to another level. We can't see what's going on inside microprocessors, but we can see the output and get more information when something goes wrong. With a dropped relay, we don't know what the circumstances surrounding it were; we just know that the train stopped. Microprocessors tell us why."
These high-tech systems include diagnostic or troubleshooting features that help keep the level of maintainability similar to that of older systems.
Consider vehicle doors. It's not essential to use a microprocessor to control door operation. "But if there is a door problem enroute, the crew must know how to correct it because the train won't move until the door is closed--that's where diagnostics come in," says Dietz. "A door light may indicate if a door is open or closed, and newer train networks can tell the crew exactly which door has a problem through microprocessor-based monitoring and communications. This way, they don't have to walk through eight or 10 cars to find out where the light is on. They'll know instantly where it is and can solve the problem."One of the main benefits of microprocessor technology is its reliability. Older systems, while easier to fix, had to be repaired more often, according to Dietz.
But when microprocessors fail, troubleshooting is much more complex. "You can't just swap out parts and hope you've fixed the problem," says Michael Hubbell, vice president-maintenance for Dallas Area Rapid Transit.
That's why maintainer training is critical. As technology changes, staff must fully understand the nuances of how systems and software work, and testing and evaluation of performance should be refined. Otherwise, when warranties are up, transit agencies will be in for a headache, according to Paul Messina, superintendent-rail transit investigations for MTA New York City Transit and chair of APTA's Rolling Stock Equipment Technical Forum.
