DutchRailnut wrote:the speed indicated by signals take effect when locomotive passes the signal.
with some signals indicating a speed for next signal. like at a medium, which indicates prepare to stop at next signal.
Some signals (under NORAC rules at least) require slowing down BEFORE the locomotive passes the signal...for example
Medium Approach: Proceed prepared to stop at the next signal. Trains exceeding Medium Speed must begin reduction to Medium Speed as soon as the Medium Approach signal is clearly visible.
Medium Approach Medium: Proceed at Medium Speed until entire train clears all interlocking or spring switches, then approach the next signal at Medium Speed. Trains exceeding Medium Speed must begin reduction to Medium Speed as soon as the Medium Approach Medium signal is clearly visible.
If for example, you get an approach medium to a medium clear, the approach medium is telling the engineer to "begin reduction to medium speed as soon as engine passes Approach Medium signal" So by the next signal, a Medium Clear, he would be at Medium Speed (usually 30mph).
However, unless required by a previous signal to operate at Restricted speed, once the next signal is clearly visible, or if the train is crossing over under say a Medium Clear or Limited Clear (among others) the "next governing signal" rule (NORAC rule 243) applys, which would allow trains to operate in accordance with the next signals indication. So say if following a train, and the engineer passes an Advance Apporach signal, and the next signal is an Appraoch. If that Approach Signal upgrades to an Advance Appraoch before he gets to it, the engineer would no longer be required to operate under the rules of the Advance Approach signal that he passed, becuase the next signal is clearly visibile, and that signal is now an advance approach. Or if say the engineer was running under an Approach or Advance Appraoch, but the next visible signal popped up to a Clear, the engineer could in crease his speed back up to MAS, again, so long as the next siganl is clearly visible.