Weather and the Railroad

A couple of years ago, during the first good snowstorm we had while I worked for the railroad, I was asked if the railroad took snow days the way some local businesses do occasionally. I think I laughed out loud. The question was an indirect way of asking if I would have some time off as a result of the snowstorm, which would not happen. More recently I was reading an article online about service disruptions to Chicago's commuter rail system during the "polar vortex" that a large part of the Midwest experienced last month. The article was informative but gave only very basic information, but the commentary by other readers is what intrigued me. One particularly upset reader commented that Metra needed to learn how to provide adequate service and stop using the weather as an excuse every time something goes wrong. Now, I do not use Metra, nor am I involved with their public relations department, but the weather can and often does play a significant role in railroading, although the consequences of the weather may be a little less obvious than other forms of transportation.

Since it is February, and still the middle of winter for half the world, we will talk about winter weather. For most forms of transportation, snow and ice can wreak havoc on roads, runways, and basically any surface over which a vehicle operates, by making that surface quite slippery. The same is true for trains, but since trains are on rails, which serve as a fixed guide way, the results are quite different. While cars might slide off the road, trains will generally stay on the rails, although stopping and starting distances will be longer. When snow gets above the rails, it also can decrease the effectiveness of the brake systems. As the wheels travel over snow covered rails, they warm up, and snow sticks to them. Most trains rely on a brake shoe contacting the wheel tread to slow the train. When released, the brake show is very close to the wheel, though not touching it. The snow that the wheels pick up gets stuck to the brakes as the wheels rotate, and it can build up and create a thick layer of snow and ice between the brake show and the wheel. When the brakes are applied in these conditions, the snow and ice must melt off before the brakes become effective. Typically in these conditions, and engineer will set the brakes periodically while running to help curb the build up of snow and ice on the brakes, but some buildup still occurs.

Snow and ice can also affect the brake system in a very different way if any is allowed to enter the air hoses. A large enough amount can create a blockage in the brake pipe itself, interrupting the normal flow of compressed air through the brake system. This situation prevents the normal application and release of the brakes throughout the train. The portion of the train behind the blockage would not respond to any of the engineer's brake operations. If this is a small portion of the train, it may go unnoticed, but if a significant tonnage is behind the blockage, the results could be catastrophic. The chances of such a blockage occurring can be reduced dramatically by blowing snow out of air hoses before coupling them when the train is first assembled. Doing proper brake tests and inspections also helps to catch this condition before it becomes a major problem.

Brake pipe blockages are one problem caused by snow and ice entering the brake system, but even a much smaller amount of snow and ice can cause problems. It is possible that an amount of snow and ice would enter the brake pipe but would be insufficient to block the brake pipe. However, it could get into the control valves on a car and compromise the brakes there. Each car on the train has a control valve, which is basically the brain for that car's brake system. It responds to changes in brake pipe pressure and applies or releases the brakes on that car accordingly. See our air brake page for a more detailed description of air brake system functionality. Inside the control valve is a pair of slide valves, which each work to apply or release the brakes. The slide valves have holes to allow air to flow from one part of the system to another, as necessary for the application and release of the brakes. These slide valves are fairly small, only a couple inches in diameter and a few inches long. The holes are much smaller, some only the size of the head of a pin. It takes very little snow to plug one of those holes and prevent proper air flow. Depending which hole or holes get plugged, the result could be anything from a brake that responds slowly to one that does not apply, or one that does not release. In a long train, a single car not applying is actually not much of a problem usually, however a brake that refuses to release can become serious. If a car is dragged with the brakes applied, the wheels heat up. If the problem goes unchecked for long enough, the wheels can heat up enough to weaken or even destroy them, which can lead to a derailment. If the brakes remain applied hard enough, the wheels may not even turn when the car is moved. As they slide, the rails will wear flat spots in the wheels. Again, if this problem goes unchecked for long enough, it can also result in derailment. One of these days I'll write about the derailment I had that was caused by brakes stuck applied.

Snow and ice are not the only challenges to the railroad during the winter. Actually, the temperature can be a pretty significant challenge as well, particularly extreme temperatures. Before we get to that, let me explain a characteristic of the air brake system though.

On a train, compressed air is pumped into the brake pipe to charge the air brake system on each car and release the brakes. The brake pipe runs the entire length of the train. On the way, the air passes through steel pipe that is attached to the frame of each car and through flexible rubber air hoses that connect the brake pipes on each car. There are countless couplings, fittings, gaskets, and valves that make up the brake pipe. Each valve, fitting, gasket, and coupling is an opportunity for air to leak out of the system. Leakage is normal, up to a point. Since significant leakage can affect the ability of the brakes to function properly, it is measured before a train leaves its initial terminal. There are limits to how much leakage is acceptable. On long trains, the effect of the leakage can be more noticeable. On a train that exceeds a mile in length, it is fairly common to have a pound of two less air on the rear compared to the head end. A couple of pounds makes no noticeable difference in brake system functionality, and it is nearly impossible to avoid. In the summer, when the weather is warm, leakage is minimal, because everything seals up properly. However, as the temperature drops, all those fittings, couplings, hoses, and gaskets tend to shrink up, and as they do so, more leakage occurs. Rubber gaskets become very hard and do not seal couplings nearly as well as in warm weather. The more extreme the cold, the more extreme the leakage.

In addition to brake pipe leakage, when air leaves the compressor on the locomotive, it is fairly warm. As it is pumped into the main reservoirs and into the brake pipe, it cools off and becomes more dense. Essentially, a volume of air at room temperature takes up much less space when cooled zero degrees. However, if it must fill the same volume, such as a brake pipe, it still fills it, just at a lower pressure. The combination of colder air and increased brake system leakage means that train length gets limited. In the cold it takes longer for the air brake system to charge, and longer for the brakes to release. It is simply impossible to build the same long trains and expect the brakes to work properly when it is extremely cold outside. Just as a comparison, in the summer in Alaska, Alaska Railroad often runs trains that exceed 8,000 feet in length. Temperatures are warm and it takes less than a minute to apply or release the brakes on a train of that size. In the winter, when temperatures in Fairbanks can dip to -60 or lower, it becomes difficult to operate a train that is 2,500 feet long. The brakes respond much slower, and charging the system, or filling it with air, can take hours instead of minutes.

While trains might not be at much risk of sliding off their intended route of travel during snowy or cold conditions, they face other challenges. The nature of an air brake system is such that it operates better in warmer weather. Many of the measures the railroad takes during the winter are preventive. Whether newspaper readers in major cities want to believe it or not, winter weather has a very real and significant effect on railroading, and is a perfectly legitimate reason for making certain service changes.