Safety First: Implementing New Rail Communication Standards

New Positive Train Control (PTC) standards bring challenges in enabling constant, reliable, and robust data links across thousands of miles of track.

The rail transportation industry, both passenger and freight, has experienced some significant accidents and near misses in recent history. This has prompted not only the owners and operators of North American railroad systems, but the government as well, to take steps to improve safety on and around the rails.

The U.S. Government has issued a mandate that Positive Train Control (PTC) systems be implemented for use across the railway industry by December 31, 2015. This primarily applies to the Class 1 freight rail transportation companies, but the passenger rail organizations also see it as important to implement. The purpose of PTC is to monitor and control train movement to provide increased safety. This is achieved by making sure that movement authorities have current information detailing every train’s location and where it is allowed safe passage. This is not to say that safety systems have not been in place for rail systems throughout history. They indeed have. However, as rail systems have expanded and there is shared use by freight and passenger services, the need for interoperability of safety and proactive communications systems is highlighted as being even more essential, as is ensuring signal integrity throughout various environments. Signal strength can be impacted by natural and man-made geography as well as the proliferation of various other types of wireless signals.

For those who are not already familiar with Positive Train Control and its goals, we’ll review those first, then dive into the challenges that the industry faces to be able to successfully achieve implementation in the currently mandated time frame.

Positive Train Control (PTC) Goals
According to the American Railway Engineering and Maintenance-of-Way Association (AREMA), the goals of PTC are to:

  • Prevent train-to-train collisions, train separation and derailment
  • Enforce train and line-speed restrictions
  • Provide safety for road and railway workers
  • Prevent movement through misaligned switches

In order to achieve these stated goals, PTC depends on reliable and robust wireless data links between train and wayside equipment, train and network access points, and waysides and network access points. The challenge is enabling that constant, reliable, robust data link across thousands of miles of track across the nation that are subjected to diverse environmental elements (natural and technological).

The Lilee Systems TransAir PTC-3000 family of 220 MHz locomotive and base station radios are designed to capture the interoperability needs of a reliable and robust end-to-end PTC solution.

PTC Elements
Let’s walk through what the elements of a PTC system are from locomotive, to wayside bungalow and crossing signals, to base station and the back office. We can think of these as elements of an end-to-end communication network where you have access points, pre-aggregation and aggregation points, the core, and the application layer.

Access point
The onboard locomotive PTC radio systems use a combination of 220 MHz radio frequencies, Wi-Fi and cellular networks as the access points. They enable the back office to communicate with the train and gather the needed information for the back office teams to make key decisions affecting the locomotive and the overall railroad network on which the trains run. The onboard PTC radios communicate with the wayside and base station systems and are recognized by the mobility controllers in the back office as they are seamlessly handed over from one service area to the next.

Pre-aggregation and aggregation
These include the systems that are in the bungalows and base stations located alongside the railroad tracks that pull in the data that’s constantly gathered by the onboard locomotive PTC systems. The data networks available from various cellular providers also are part of the aggregation layer. Together these systems and services make sure that the communication link to the back office stays up so that the data and the locations of the locomotives has no holes. Through this point in the overall PTC end-to-end communication system, system monitoring and alerts can be passed to the locomotives, enabling a further optimized proactive communication method.

The Lilee Systems WMS-2000 Wayside Messaging Server provides an interoperable communications gateway platform for Positive Train Control systems. This Red Hat enterprise Linux (RHEL) 6.2 hardware-certified system runs the ITC messaging system between local wayside interface units (WIUs) and the communications network in an interoperable train control architecture.

This can be thought of as the cloud where the rail big data makes a stop before being accessed by the application layer.

Application layer
In the case of rail operations, this is the back office where the dispatchers are located. It is here that the complete end-to-end solution comes together. Dispatch teams must have up-to-the-minute information about where passenger and freight locomotives are on the entire system. The systems that make this information available need seamless access to train data. They must be capable of maintaining a permanent virtual tunnel to the locomotives and pull in data quickly over the appropriate available channel, whether that be through Wi-Fi, 220 MHz or cellular data. The added capability of remote configuration, management and update from the back office mobility control system offers further resources for the PTC solution.

The Lilee Systems LMC-5500 Mobility Controller handles registration of the radios, plus provides remote configuration capabilities and continuous monitoring even when the radios are roaming and moving at high speeds, all without a back office team member being aware of the underlying network topology changes as the rolling stock moves from segment to segment.

PTC Implementation Challenges
Now that you are familiar with the elements of the PTC end-to-end communication network, we can address the implementation challenges and evaluate the means for resolving them.

As mentioned previously, various old systems have been used across the railroad system in the past. The challenge is that they didn’t all communicate well with each other. They were not interoperable with the network elements from one operator to the next. So the picture of rail usage that they painted wasn’t complete, leaving some holes indicating unknowns about rolling asset location, status, speed, etc. The PTC mandate intends to try to resolve this by giving clearer direction about protocols to use as well as communication frequencies. However, no absolute definition for interoperability has been established. Some Class I railroads are implementing I-ETMS. Others will use ITCS. The third type that is being implemented is ACSES. With respect to system solutions to serve these different methods, they ideally could handle all of them and be able to dynamically identify what to use when in certain territories.

The frequencies to use and their availability are other challenge points for PTC implementation that may cause a delay and push the implementation cost beyond original estimations. PTC identifies 220 MHz as the frequency to use and Class I railroads have tried to procure use of this in as many areas as possible. Also, this frequency is close to others and as a result is sometimes subjected to interference from the adjacent frequencies, resulting in diminished signal integrity. If the PTC system has implemented the radio as a software-defined radio (SDR), adjustments to account for these interferences can be made via software modifications and additions that are more cost-effective. However, if the solution is not SDR-based, then implementing hardware filters to handle the identified interferences can be costly. The other alternative of adding additional base stations is even more cost-prohibitive. Worth noting is industry talk of the need to use more than a single radio frequency. Therefore, solutions that are capable of operating on different frequencies such as 160 MHz and 900 MHz offer a better match to current a forward-looking industry requirement.

A working group within IEEE is working to propose a comprehensive solution to the wireless component of PTC: 802.15.4p. The objective of the pending open standard is to provide a pathway toward a more interoperable, robust, reliable, future-proof, and scalable solution for the wireless component of PTC.

It is likely that PTC will continue to evolve as the rail industry for both freight and passenger transportation works its way toward implementation. As they identify additional functionality that they’d like to achieve with PTC both for safety and optimized business operations, the solutions that have flexibility built in and can add in the newly identified requirements will be best suited to serve the needs of the industry for the long term.



Christine Van De Graaf is the product strategy manager for Lilee Systems. Christine has over a decade of experience working in the intelligent systems and embedded computing technology industry and holds an MBA in marketing management from California State University, East Bay.

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