I recently took Amtrak’s Capitol Limited train between Washington, DC and Chicago. Much or all of the intercity travel was on a dual-track line, in that there were two tracks, and we passed many many freight trains headed the other way.
One thing that I noticed was that the train would “switch” occasionally between “right” and “left”, relative to the direction of travel. When we were on the right, trains passed us in the opposite direction on the left, and vice versa, so when we were travelling on the left, trains passed in the opposite direction on the right.
Why all the side switching?
I speculated that it might have to do with load balancing, if trains tended to be heavier going in one direction than the other, to ensure that the rails wore down more evenly.
What’s the straight dope?
Probably track wear is not a major consideration in routing tracks from track to track…
The dispatcher on that line controls the track the trains run on, and while there is generally a ‘preferred’ direction of travel (in North America, it generally is ‘keep right’ much like auto traffic, although historically some railroads like the Chicago & NW had left hand running), double track is often bi-directionally signalled, so that a passenger train (which is supposed to have superior rights to freight - i.e. precedence - this is not always true in practice) can bypass a slower freight train (or a local freight that needs to access a siding diverting from the right track, or a slow moving local commuter train - whatever) via left hand running.
The goal is to always keep the trains moving, and superior trains (Passenger, ‘hot-shot’ intermodal, etc) are assigned more rights over slower trains (like a low-speed coal unit train) - this is the goal, at least.
Agreed. The track switching was almost undoubtedly done to facilitate a better traffic flow, for both your train and other trains on the line.
It could be any number of things. Railroad dispatchers, like air traffic controllers, play a sort of high-stakes video game, constantly shuffling heavy, fast-moving objects and scheduling movements down to the second. Some possible reasons for the frequent switching of sides:
A) Passenger trains are generally shorter and lighter than freights. “Switching sides” generally involves a slowdown and a passenger train can accelerate back up to speed much more quickly.
B) The relative length of passenger & freight trains may have played a role - the distance between crossover switches may not have been amenable to switching the longer freight.
C) Track on one side or the other may have had some maintanence-related speed restrictions which would have delayed the passenger train while the slower freight could accomodate them without damage to its schedule.
D) While trains from the other direction may have been more obvious, you were almost certainly passing around slower trains headed in the same direction also.
E) Track on one side or the other may have had some clearance restrictions that the passenger train could accomodate but the freight trains needed to avoid by using the other side.
Could have been any of the above, or any number of other things as well. In earlier times, before the advent of centralized dispatching, double-track lines often were “dedicated”, i.e. directional. Commonly they were designed for “right-hand running” like a highway, IOW traveling on the right-hand side dependent on the direction of operation. Improvements in communications and signaling enabled bi-directional operation and greatly improved the operating efficiency of railroads.
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Which is why the signs around station platforms tend to say things like: “Warning. High speed trains may approach on any track from either direction”.