Striking a balance for weather-resilient railroads

Posted by Malcolm Kenton
on Monday, June 10, 2019

After reading the comments on my previous column about the shortcomings of Positive Train Control and weatherproofing signal systems, doing further reading and consulting with knowledgable sources, I’ll admit that my conclusions drew on a limited understanding of how signal systems work and of the true complexity of what it takes to make them less susceptible to failure in heavy rain and other weather events. 

I did not intend for my words to be interpreted as in any way denigrating towards front-line rail infrastructure and signal system designers and maintainers. These individuals’ laudable work is constrained by the limited resources granted and priorities assigned by management, whose decisions are in turn shaped by political decisions made by Congress and administrative agencies. It is these higher-level influencers whose focus must adjust if we are to arrive at a more permanent fix for the issues described in my previous column. The design of effective means of managing railroad traffic is always a matter of balancing safety with speed, fluidity and other criteria while giving safety the most weight.

Diagram showing how track circuits detect trains, from the Electric Power Research Institute's 'Power System and Railroad Electromagnetic Compatibility Handbook, Revised First Edition' (Nov. 2006).
The signal indications that govern train movement are determined by circuits in the running rails that detect the presence of steel wheels on the rail. One or more of these circuits makes up a block, and the detection of a steel-wheeled vehicle within the block automatically changes signal aspects so as to prevent other vehicles from entering the block — dispatchers do not control this process. 

Any time a track circuit is interrupted, the system will act as if that block is occupied and will cause restrictive signals to be displayed so as to prevent the movement of other trains into that block. Unfortunately, the signal system cannot tell the difference between pressure exerted by the wheels of a train and that exerted by water saturating the ballast beneath the rails. Therefore, after a heavy rain on a track section with poor drainage, or during flooding, the system may falsely indicate that a block is occupied. 

Lightning can also disrupt track circuits and cause signal failures. Most railroads have installed lightning deflection devices on signal cases or bungalows, but the rails themselves can act as lightning rods, and this is near impossible to mitigate. When a circuit is disrupted, the operating crew of any train passing through the affected block(s) must stop at the signal and receive permission from the dispatcher over the radio to proceed at a restricted speed, generally 15 mph. This is what happened to my westbound Cardinal three weeks ago as it passed through thunderstorms at the north/west end of the New River Gorge.

There are a number of measures that could prevent this type of disruption from happening as often as it does, but they all cost money. Most railroads’ management have, for better or for worse, concluded that capital expenditures are more effectively allocated elsewhere. One such measure is improved ballast drainage — ballast will not become oversaturated if rainwater has somewhere else to go downhill. But it is costly to design, operate and maintain effective drainage techniques, as these vary greatly by context, climate and geography. Climate change’s effects exacerbate this challenge.

'Rain on the Plains,' taken June 1, 2015; location unspecified. Photo by Flickr.com user railsr4me.
The latest advances in track circuit technology, such as mechanically and electronically-coded circuits, help train control systems operate more reliably by allowing track circuit energy to promulgate over a greater distance, thereby minimizing the likelihood that “low ballast” conditions will cause blocks to be falsely shown as occupied. The challenge with broadly implementing these solutions is that they require an entire line, generally an entire subdivison, to be upgraded at the same time. These technologies are being put in place on more lines, but the places where soggy ballast most routinely slows trains down to a crawl are usually those where management has determined that its benefits to operations are overshadowed by its cost. 

A third potential solution is to shorten the length of track circuits by installing a ‘cut section,’ thereby replacing one circuit with two. But this is also costly, as it entails putting in more insulated joints, wires and bungalows. Much of the budget that railroads might have put towards signal upgrades like this, as well as other capital improvements, has instead gone towards installing PTC to comply with the federal mandate. 

PTC uses means other than track circuits to locate trains and determine their speed and other characteristics. This groundbreaking innovation could have been implemented as a replacement for legacy signal systems, which would have delivered a number of operational benefits to railroads. Unfortunately, in part owing to the narrow way in which the 2008 law was written, railroads are implementing PTC only as an overlay to their existing signal systems to enforce their most restrictive indications. Therefore, any structural weaknesses impacting the current signal system also underlie PTC.

Holistic thinking needs to be done about the appropriate level of investment and the most effective techniques for allowing railroads to maintain schedules and fluidity in the midst of more frequent storms, floods and other troubles posed by a warming planet and disrupted weather patterns. The challenge will be getting both the public and private-sector actors who have the power to alter the industry’s course to come to a constructive agreement that does the utmost to maximize safety without giving short shrift to other measures to help the rail industry thrive and grow, attracting more travelers and shipments off of the highways.

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