What's the distance between signals
What's the distance signal's aspect
What's the type of signal, Absolute or Permissive
http://www.railroadsignals.us/basics/basics4.htm
There are a number of "speed" terms associated with signals and the rules. Some speed terms are associated with just signals, and others are used in instructions by the dispatcher
The following terms are taken from a
Southern Rwy rulebook and a
Conrail signal card. There may be additional differences on other railroads.
1) Normal Speed: The maximum authorized speed.
2) Limited Speed: A speed not exceeding 45 miles per hour. Some railroads, such as the New York Central (aka: CR) specified 45MPH for passenger trains, and 40MPH for freight trains.
3) Medium Speed: A speed not exceeding 30 miles per hour.
4) Reduced Speed: Proceed prepared to comply with flagging signals and stop short of train or obstruction.
5) Restricted Speed: Proceed prepared to stop short of another train, obstruction, or switch not properly lined and look out for broken rail, but at a speed not exceeding 15 miles per hour. Conrail specified 20MPH outside interlocking limits, and 15MPH inside.
6) Slow Speed: A speed not exceeding 15 miles per hour. Some railroads have pushed this up to 20MPH, such as CSX.
7) Yard Speed: A speed that will permit stopping within one-half the range of vision
.
John