Simplifying Signal design

Railway Age, August, 2000 by William C. Vantuono

"Geographic signaling" makes the complex task of designing signal system logic a little easier.

You're a railroad signal engineer, and you've just spent several months designing the circuitry and incredibly complex computer logic for a massive main line expansion project. You've got all the bells and whistles built in that will make your railroad run smoother and faster than it ever has: several new microprocessor-controlled interlockings, a state-of-the- art reverse signaling system, constant-warning-time grade crossing predictors--the works. You proudly present your voluminous signal design plan to the chief engineer, who's been equally busy planning for this main line event.

A week later, your plan comes back to you. A lot of things, you're told, have been changed, including several key interlocking locations and configurations. Is it back to the drawing board? Do months of design work get tossed into the round file? Do you start from square one (after privately thinking about going to work for a supplier)?

Take heart, all you beleaguered signal engineers. Safetran has introduced a new way of designing signal systems and their inherently complex logic. It's called GEO [TM], for Geographic Signaling, and according to Safetran, its developer, it promises to revolutionize the C&S function.

The first installation of GEO will be on Canadian National's River Subdivision in Manitoba. CN is installing 80 miles of CTC, replacing pole lines with spread-spectrum data radio and installing microprocessor- based interlockings and coded track circuits. GEG will be installed on an intermediate (between sidings) location. Details are being finalized for an installation on Union Pacific, and discussions have begun with a third railroad.

Goodbye, Boolean logic

Basically, GEO turns signal system design into a "drag and drop" exercise using a graphical computer interface (sidebar, p. 62). You create a track diagram--an interloclting, for example--placing "objects" (signal heads, turnouts, etc.) where they need to go. GEO does the rest, automatically generating the required signal logic. "You can look at your chief engineer and say, 'You didn't get me this time,'" says Safetran General Manager-Marketing and Technology John Sharkey.

Safetran Vice President-Technology Bill Petit explains GEO like this: "It uses a new technique whereby the signaling logic is embedded in individual 'objects' rather than requiring the equivalent of relay, Boolean, or ladder logic design for interlocking controllers and plants."

Safetran began GEO's development process by identifying some of the problems that needed to be solved in installing a train control system. "Long design times have been made worse lately by a shortage of engineers skilled in application requirements," says Petit. "A new approach was needed to dramatically reduce design time as well as use available expertise across a wider number of projects. As microprocessor-based systems became widely accepted, application testing became more and more complex. This is particularly true for changes made to existing installations, because they required the complete application to be re-tested. Isolating the modified section to reduce re-testing became a major design requirement. It's also essential that new systems allow a clear migration path to future technology."

Petit says a building block approach was needed that would allow railroads to move from conventional signal systems to more-sophisticated PTC (Positive Train Control) without a major change in wayside infrastructure or a major capital investment. Railroads have also been wanting tools for real-time as well as predictive signal system maintenance. "A geographic, object-based approach to train control systems was the best way to address these problems while still maintaining the reliability and safety demanded by the railroads," says Petit. "Accomplishing this required 'out of the box' thinking."

GEO identifies individual objects like switch machines, signal lights, and track circuits. "Incorporated into each of these objects are all the 'rules' of train control, to provide all the needed safety and operational attributes," says Petit. "Using a graphical computer-based configuration tool, these objects are then dragged and dropped into place in the track layout. High-level messages (computer logic) are exchanged only between each object and its immediately adjacent objects. As such they need no knowledge of the overall architecture of the railroad."

This approach can be contrasted to existing signaling design, adds Petit, "whether it be via relay logic, Boolean logic, or ladder logic, which requires detailed knowledge of each application."

GEO's object-based approach "provides great flexibility," says Petit. "Since objects are independent of a complete system layout, individually-addressable, and communications-based, different ways of interconnecting them are possible. GEO's objects utilize open-architecture interfaces based on ATCS messaging concepts. They allow for flexible block-type operation in areas where maximum train capacity is needed. And since they're individually-addressable, their health information can be tracked."