Safety First: Implementing New Rail Communication Standards
A working group within IEEE is developing a proposal for the wireless component of Positive Train
Control (PTC) to develop a more interoperable, robust, and scalable solution for improved train safety
Christine Van De Graaf, Lilee Systems
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).
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.
[Insert image of the Lilee PTC-3000 family of Locomotive Radios]
[Caption: 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.]
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.
[Insert image of the Lilee WMS-2000 Wayside Messaging Server]
[Caption: 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.
[Insert image of the Lilee LMC-5500 Mobility Controller]
[Caption: 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 SDRbased, 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.
Bio: 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.
Pull quote: 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.