Freight Trains, Distributed Power and Process Safety
In a recent series of posts, we noted that there seem to be an increasing number of accidents involving freight trains in the United States. The latest post — Tank Cars: Process and occupational safety — suggested that the response to these events have been mostly to do with occupational safety. (The issue that receives the most attention is train-vehicle collisions.) Yet, some of the recent accidents have involved a release of process chemicals, including vinyl chloride, chemicals created when vinyl chloride burns, and ethanol. The management of tank cars carrying highly hazardous chemicals requires the application of the principles of process safety.
A recent report from the Associated Press — Regulators say railroads must examine how they build trains — describes how regulators are looking at systems issues, i.e., they are developing a process safety way of thinking. The report states,
Heavy cars at the back of a train can push and pull against empty cars in the middle of a train as it goes over hills and around corners. Those forces have become more of a problem as the industry increasingly relies on longer trains with a wide variety of freight aboard.
Another factor complicating the issue is the industry’s practice of placing locomotives throughout trains. The locomotives can amplify the forces if they’re not used correctly.
I live on the east coast mainline. I see these trains go by all the time. A few years ago CSX (the freight company that owns and operates the tracks in this area) started putting locomotives in the middle and at the end of the strings of freight cars. The use of this technology means that the stress on the couplings between the cars can be reduced because they are not all being pulled by the head locomotives; instead, some of the cars are being pushed by the locomotives in the middle or at the end of the string. In principle, there seems to be no limit as to how long such trains can be.
The difficulty with this system is that the locomotives at different locations may not have the same power requirements. For example, the head engine may be going uphill, so it has to apply a lot of power. At the same time, the engines in the middle of the string may be going downhill, so they need to apply less power. Software manages the system so as to keep even stresses within the overall string. This practice is referred to as Distributed Power.
Therefore, the AP statement, “The locomotives can amplify forces if they are not used correctly” is correct. But there should be no reason for the locomotives not to be “used correctly” if the Distributed Power software is properly designed and operated. It should also be noted that, to the best of my knowledge, the use of intermediate locomotives was not a factor in the East Palestine, OH and Raymond, MN accidents.
The use of Distributed Power systems illustrates a process safety way of thinking. Freight trains are being managed as part of a complex system. Safety goes beyond simple railroad crossing collisions.
