There are basically three types of activities that signals impose on you:
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<li /><b>Signals that make you stop or be prepard to stop.</b>
The Stop Signal, Stop and Proceed and Restricting signals fall into that category. Basically, when you see them, come to a stop, except with Restricting, which forces you to continue at Restricted Speed <u>prepared to stop</u> short of "bad" things.
<li /><b>Various clear signals.</b> These allow you to keep going (e.g., Clear). The Limited Clear, Medium Clear, and Slow Clear require you to be at a certain speed or slower, usually because you are being diverted from one track to another and the switches that you are crossing require a slower speed.
<li /><b>Signals that slow you down.</b>To get to the slower speeds that we mentioned, you need to be forewarned early enough to allow you to slow down. Approach Limited, Approach Medium and Approach Slow, are such signals. They basically tell you to approach the next signal at a certain speed.
<li /><b>Signals that warn you about an upcoming stop.</b>These signals simply warn you to expect a stop at the next signal (or two signals down). Advance Approach and Approach are such signals. Sometimes, signals warn you of an impeding stop AND slow you down sufficiently in advance of the stop. Medium Approach and Slow Approach are such signals.
<li /><b>Oddball Signals.</b>Every list has things that don't fit anywhere else, and this is no exception. These signals accomplish other tasks. For example, Clear To Next Interlocking tells you just that: The track to the next interlicking is clear.
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There is a variety of ways these signals are used. It's usually up to the track designer to choose how to best arrange signals to permit the safe movement of trains. Here are common examples:
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You are on a high-speed track, doing, say, 80 MPH, and a certain situation down the track will require you to come to a complete stop. The signal at that location will display Stop Signal, but by the time you actually see it, it may be too late to slow down and stop safely before it. So, one signal before the Stop Signal might display Approach, warning you of the impeding stop. If that signal is located too close to the one displaying a Stop Signal, they may have wired the one signal before the Approach to display Advance Approach. So, you, doing 80, see the Advance Approach first, and know that the second signal after this will require you to stop. So you start slowing down. Then you see the Approach, which tells you that the next signal is at Stop, so you slow down even further. By the time you reach the actual Stop Signal, you ae going slowly enough to be able to stop with no problem.
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Another example is being diverted at an Interlocking. Let's say in our previous example, that you will need to cross over from one track to another. The crossover there requires you to move at 30 MPH, which is Medium Speed in NORAC. So, by the time you reach the crossover, you must be doing Medium Speed. To do that you will need to be slowed down. First you see an Approach Medium signal. It tells you to approach the next signal at Medium Speed. So, you begin slowing down. By the time you reach the interlocking, its home signal shows