Advanced Civil Speed Enforcement System - Redundancy

Redundancy

There are a number of redundant components in the overall ACSES system such that a failure of a subsystem will swap over to another automatically. The loss of a WCM, for example, due to a power outage or lightning strike results in a standby WCM taking over the communications duties between BCMs and the office systems.

Because a locomotive's radio is capable of being heard by a number of BCMs, the WCM examines the indication RF signal strength of each BCM that heard the locomotive to determine what the strongest talk path back to the locomotive is. The WCM maintains a record of three possible talk paths to the locomotive such that the strongest path is always selected if the office needs to communicate back to the locomotive.

As a locomotive moves from region to region, the radio signal strengths recorded by BCMs which get conveyed to the WCMs change. BCMs which fall out of range of locomotives are removed from talk path routes within the WCM in favor of the BCMs which are coming into range. In this way the WCM is constantly aware of where each locomotive is located and which talk path is best used to communicate with the locomotive. Such information is also conveyed to the office so that office systems may make use of it.

Another aspect of redundancy is the system design which looks forward along the track, acquiring TSRs for the future in the event a temporary communications failure occurs. Since each locomotive has TSRs for at least three future segments of the rail line, in the event there is a segment of the track which for some reason has lost radio communication to the office, the locomotive has TSR information for the "dark" segment already before it proceeds into the dark segment.

In the event of a loss of all redundant standby systems (such as might occur due to a wide area power failure or communications failure with the central office) the system will indicate to the locomotive engineer that it has lost the ability to enforce temporary speed restrictions, but the permanent restrictions loaded into the on board database will continue to be enforced.

Finally, the cab signals are considered a completely independent system that transmits a continuous stream of codes through the rails instead of via wireless transmission. Any fault in the ACSES overlay will not affect the cab signal system and moreover a cab signal failure will not affect the ACSES system. Without cab signals ACSES will continue to enforce positive stops at absolute signals, all permanent and temporary speed restrictions and a positive stop at any signal at the entrance to cab signal without fixed wayside signal territory that is not displaying "Clear to Next Interlocking."