The question now becomes: How do you update legacy microprocessor-based and relay-based wayside signal locations with the latest technology while minimizing disruption to existing operations? This can be challenging, especially given the fact that legacy systems typically have limited critical computing resources such as bandwidth, memory, communications capabilities, etc.
Each one of the pieces of equipment that is on a PTC-affected area of track, whether it’s a legacy relay location or a modern microprocessor, HAS to be upgraded. It has to be upgraded because of the functionality of PTC’s interoperability mandate. The new wayside systems will need to be installed so that:
• Disarrangement does not occur. In other words, a proposed solution cannot disrupt the current system. Disarrangement of an existing signal location would require extensive retesting which would increase the amount of time and resources required to implement PTC functionality.
• The amount of field labor required is kept to a minimum
• The amount of engineering design and back office support is kept to a minimum
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Typical signaling systems that are currently installed
throughout the United States direct and control trains for
the speed and route through solid state or relay based
wayside equipment. The wayside equipment communicates
to the locomotive through a lamp (or aspect). Different
color lamps mean different things to a locomotive engineer.
Current wayside systems control trains on the railroad and
give vital lamp aspects to the locomotive engineer. With
the Rail Safety Improvement Act and PTC mandate, in
addition to communicating through a lamp to a human
being, these signal aspects are communicated continuously
to the train – therefore anther layer (PTC) has been added to the requirements. With PTC, the wayside device gathers information from the signaling equipment – whether it be a switch, lamp or track circuit - and determines what the signal should be showing. Additionally, PTC utilizes the signals that are currently displayed and packages that information into a digital message. That digital message or Edge Messaging Protocol (EMP) is then being communicated to the locomotive.
The wayside system is taking the existing information that is inherently there and summarizing it into an aspect and communicating that information vitally to an onboard system. This takes the element of human error out of the equation by putting fail-safe systems in place in case the engineer misses or fails to see the current lamp (aspect) that is in place. If the engineer misses the required action, PTC will enforce it; whether it’s slow down to a certain speed or stop altogether. Either the onboard system or the engineer will make sure the locomotive adheres to what the locomotive should be doing. As long as the engineer doesn’t miss anything, the onboard system will not need to kick in. If the engineer deviates from what he should be doing –by an unsafe margin the onboard system will then take over to correct the train.
Today, there are more than 100,000 wayside signal devices on rail lines throughout the U.S and Canada, and the majority of the microprocessor-based version were manufactured by GE/Harmon. The age and functionality of many of these systems vary greatly depending on location, railroad and time of purchase; Some of these units may have been in operation since the early 1980s. These products are extremely reliable and in many cases are not near the end of useful life. There are also many existing relay-based locations still in operation that are up to 70 years old.
