A definition, by definition, is not a rule. Railroads developing the rule governing trains operated at restricted speed add several different "advisories"-- "looking out for..." an improperly lined switch, a broken rail, another train, or engine, or obstruction, malfunctioning crossing protection etc. The list of possibilities is endless, and that's the point of "restricted speed" and why, in fact FRA's definition is at one and the same time so spare and so all-encompassing
What counts of course, is, and is only the "permit stopping within one-half the range of vision."
What counts is the crew's responsibility for complying with the conditional authority for the movement of the train.
Once in awhile, someone, usually younger than me (which is almost everyone) asks me why some railroads include something like "prepared to stop at a stop signal" and why some others don't? And my answer is a definitive "I don't know."
I do know that I was "brought up" on railroads that did not include the "prepared to stop at a stop signal" proviso, and that made, and makes, perfect sense to me. The "prepared to stop at a stop signal" stuff.....? Not so much. Let me count the reasons:
1. Restricted speed exists separate and apart from a restricted speed signal. By which I mean not only that restricted speed is mandated in territory where automatic block signal systems and rules are not in effect.
2. A restricted speed signal is not necessarily, nor usually, an "advance" or "distant" signal to any other signal indication. Historically, a stop signal is "pre-indicated" by the approach signal distant to it. In fact, once upon a time, I recall the rule regarding an approach signal as going something like "Proceed not exceeding medium speed prepared to stop at next signal. Reduction to medium speed must commence before engine passes Approach signal." That's from memory so maybe I missed something. In any case, the "restricting" signal is not driven by a positive stop indication.
3. But most of all, I don't get the "prepared to stop at a stop signal" because a) that's included in prepared to stop within half range of vision. It's no more necessary than advising the crew to be prepared to stop short of a refrigerator, sofa, Toyota, or other locomotive b) "restricting" is a permissive signal authorizing movement and a stop signal is the end to that authority, and to all authorities for movement that a train may have.
Well, call me old fashioned but I think that "restricted speed" was, is, and will always be intended for something other than indicating a positive stop ahead.
Restricted speed is determined by conditions other than the next signal indication.
In signal territory, it can be triggered by occupancy of the block in advance of the signal. In these circumstances, we have to remember the limitations of the block signal in determining the three most important components of safe train operations: location, location, location.
The block signal system, the closed track circuit, cannot determine the location and the physical extent (length) of the condition of occupancy. Therefore, while in all our other endeavors we work (and worry) assiduously to prevent any possible "lapping" of authorities, in these circumstances, we deliberately allow an overlap of authorities...up to a point...under a restrictive set of conditions.
Now I think restricted speed, and the restricting signal, are wonderful applications of railroad logic for numerous circumstances. However, these are applications based on a technology of imprecision. I don't think restricted speed is such a good idea for safe separation of trains, given the precision technology that is now available for identifying the positive limits to one train's authority, which of course is the rear end of the train ahead. Just as I don't think it's so hot that many current cab signal systems do not distinguish between (no code) restricting, and (no code) stop.
Arcane? Esoteric? Idiosychratic? Archaic? Right, everyone's a critic.
January 22, 2014
236.812 speed, restricted.
A speed that will permit stopping within one-half the range of vision, but not exceeding 20 miles per hour. --Code of Federal Regulations, Title 49