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K.P.: The old head dispatchers I've worked with, some with seniority dates back into the 1940s, all insist that OS means On Sheet. But perhaps it meant something else somewhere else -- like in the East. Alas, the bookshelves are all a bit sketchy on the origin of OS. Most of them equivocate between On Sheet and On Station. No source I can find says Out of Station. So I spent some time reviewing "Rights of Trains," 1954 edition (originally published 1904) and the rule books to see if I could arrive at a logical rationale for OS meaning On Sheet or On Station -- or maybe Out of Station. What I see in the rules is that OS from a dispatcher's or operator's point of view must refer to the front of the train, not the rear. The reason has to do with how trains were granted authority to occupy a main track in train-order days, and the fact that trains are prioritized. Trains are directional, and the direction is forward. In order to move a train, authority must extend in front of a train. The dispatcher didn't concern himself with the location of the rear of a train, because it was protected from following movements by a flagman as well as the 10-minute separation between following trains. At a meet, the rear of the train is self-protected, because the inferior train could visually verify that the superior train hadn't cleared the meeting point. The highest priority train on a railroad is the first-class passenger train. By rule the trains running in one direction are superior to trains of the same class running in the opposite direction. Thus the entire railroad runs off the schedule of the first-class passenger train that runs in the superior direction. That train shall not be delayed, so the dispatcher wants all inferior trains tucked out of the way at least five minutes before the first-class train arrives. Thus, the time that is most important to the dispatcher is the time the first-class arrives at an open station, because that's the last time from which he can subtract the first-class train's running time (plus five minutes) to the place where he can set a meet with an inferior train. It's the absolute minimum time he can take to the bank. And the meets are made by the head ends of trains, not the rear ends. But, you might ask, what if the train runs slower than expected to the meeting point from that OS point? That is not the dispatcher's immediate concern. His concern is with protecting the schedule. If he delays the train, it's on him; if the train runs slow, that's its to answer for. By setting the OS time at the front of the train, the dispatcher cuts to the minute the minimum time he must allow -- and since trains have length, and the head end gets to the meet first, wherever the head end is located is the point where time is measured. The only other thing I can speculate is that eastern railroads that ran as 251 territory, with interlocking plants controlling main track crossovers sprinkled along the route, might have been more concerned when a train left the station than when it arrived, because only after it cleared the interlocking plant could a new, conflicting, move be lined up. In that case, OS might well have meant Out of Station. Every electronic train sheet I have seen today records the time when the head end of the train hits the control point and is On Station, not when the rear end leaves. If OS ever meant Out of Station, it doesn't now on these roads. The instant in time when the train becomes On Station is also the time when the train becomes On Sheet. OS
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