12-28-2011, 10:40 PM
Quote: Signals with two heads stacked vertically are used at interlockings while signals with a single head are used as intermediate block signals. {/quote]
Not necessarily. A two headed signal in the western half of the US typically indicates a diverging aspect, which can be a control point or an interlocking. You can also have an automatic interlocking with single head signals.
Quote: Signal placement will largely depend on the era and signaling system. By American standards signals are placed on the outside of double track territory. With full Centralized Traffic Control (CTC) trains can operate on any track in both directions without restrictions. As such signals appear in both directions for all tracks on the outside of the right-of-way.
For basic block signal operation (Rule 251) signals appear only for the designated direction on each track on the outside of the right-of-way. Trains operating against the current of traffic will require specific permission from the train dispatcher to do so.
Mixing systems.
CTC and ABS (a "basic" block signal system) is signaled in both directions. Rule 251 is current of traffic which is signaled in one direction (the other direction is considered non-signalled territory).