The 1947 rear ender at Naperville is an example of how and why signals needed
to be, and were, re-aligned. Traffic density and train speed play a critical
role in signal spacing. Also, adding a greater number of signal INDICATIONS
(the operational requirements conveyed by the ASPECT [color, solid, flashing,
multiple colors, etc.] of the signal) provided higher levels of safe train
movements.
Of course, the single, GREATEST safety feature of a signal system is COMPLIANCE
with the indications.
Karl
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