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Trains’ quick glossary of positive train control terms

By Todd DeFeo | May 31, 2019

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Positive train control (PTC) is perhaps the most discussed railroad topic in recent years.

It is a broad term for a technology system designed to prevent train collisions, derailments and unauthorized train movements, including movements where workers are on the tracks.

Congress approved the PTC requirement as part of the Rail Safety Improvement Act of 2008 (RSIA). The law initially mandated railroads install PTC on tracks that carry passengers or so-called toxic-by-inhalation (TIH) materials by the end of 2015; an extension was granted, giving railroads until the end of 2018.

As of Dec. 31, 2018, Class I railroads had spent $10.5 billion on PTC development and deployment. According to AAR, Class I freight railroads had equipped 83 percent of their rail network with PTC.

“PTC represents an essential next step for the rail industry to improve safety of train operations, and it will make the entire U.S. rail network safer for passengers, railroad employees, and the cities and towns through which the national rail network traverses,” Amtrak Chief Operating Officer Scot Naparstek testified in September 2018.

The precursor for PTC dates back more than 100 years, according to the Congressional Research Office. In 1906, Congress directed the Interstate Commerce Commission (ICC), the predecessor of the Federal Railroad Administration (FRA), to explore the automatic control of railway trains and recommend legislation they thought might be necessary.

The PTC implementation process has created a new lexicon. At its core, according to the American Association of Railroads (AAR), there are three main elements of PTC:

• Back-office server (BOS): This server stores information related to the rail network on trains operating on it. This server sends data to the systems onboard locomotives.

• Onboard (or locomotive) system: This is the computer onboard the train’s locomotive. The system monitors the train’s speed and location and can apply a locomotive’s brakes if necessary to enforce compliance with speed restrictions or stop unauthorized movements.

• Wayside system (or units): These trackside devices monitor and report switch positions, signal indications and track circuits to both the locomotive and the central office.

Additional terms you may hear in any PTC conversation include:

• Automatic train stop (ATS) or automatic train control (ATC): These systems can override the engineer’s controls if the engineer does not acknowledge or abide by a wayside signal.

• Centralized control or dispatch: This central location grants authority for trains to move and implements speed restrictions.

• Communication network component: The combination of wired and wireless networks allows the exchange of messages between PTC system components, including the back office server, the onboard system and wayside signals.

• Communications-based train control (CBTC): This computer-aided dispatching framework sends train information to a central location. This location then distributes information to the network’s entities.

• Interoperable (or interoperability): There are different versions of PTC, such as Wabtec’s I-ETMS (Interoperable Electronic Train Management System). Since commuter, passenger and freight railroads must be able to operate across all railroad systems seamlessly and communicate with other railroads’ systems.

• “Overlay-type” system: Most U.S. railroads currently are implementing this type of operation in which they install sensors, signals and transponders across their existing network.

• Safety Management System (SMS): “An SMS is a proactive risk management system, which will move us toward a more predictive safety management method at an organizational level,” Amtrak Executive Vice President & Chief Commercial Officer Stephen J. Gardner explained in May 2018 testimony.

• Spectrum: Radio frequency spectrum is the bedrock of wireless communications, a key element of PTC. Spectrums are segmented into bands of radio frequencies and measured in cycles per second (known as hertz).

• Wireless data communications system: This system integrates the locomotive system, the back-office server and wayside units.

According to Union Pacific, the FRA evaluates railroads’ PTC safety plans and certifies the system after the conclusion of development and testing and before trains equipped with PTC enter service.

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