Block Signals

Automatic Block Signals are fixed signals, automatically controlled, at the entrance to a block governing trains entering and using that block.

Signals display aspects which imply a meaning or indication to the crews. Often two signal heads will be used for a given signal, providing aspects such as RED over YELLOW. There are four lamp colors utilized:

• RED
• YELLOW
• GREEN
• LUNAR (a bluish-white, but not clear)

SINGLE ASPECT SIGNALS
ASPECT	GREEN	YELLOW	RED
NAME	CLEAR	APPROACH	STOP
INDICATION	Proceed. Train may operate at maximum speed otherwise permitted.	Approach. Train must not exceed 30 mph or the maximum speed otherwise permitted and be prepared to stop at the next ABS signal.	Stop. Do not proceed into block except as permitted by [rule].

Two Aspect Signals

ASPECT	NAME	INDICATION
LUNAR or RED over LUNAR	RESTRICTING	Proceed at restricted speed. This indication will only be displayed when there is an obstruction, rolling stock, opposing or converging traffic (moving at restricted speed) or a switch not properly lined in the block.
GREEN over RED	CLEAR	Proceed. Train may operate at maximum speed otherwise permitted. Train will continue on same route at first switch beyond signal.
RED over GREEN	DIVERGING CLEAR	Proceed. Train may operate at maximum speed otherwise permitted. Train will take diverging route at first switch beyond signal (10 mph through switch).
YELLOW over RED	APPROACH	Approach. Train must not exceed 30 mph or the maximum speed otherwise permitted, whichever is less, and be prepared to stop at the next ABS signal. Train will continue on the same route at first switch beyond signal.
RED over YELLOW	DIVERGING APPROACH	Approach. Train must not exceed 30 mph or the maximum speed otherwise permitted, whichever is less, and be prepared to stop at the next ABS signal. Train will take diverging route at the first switch beyond this signal (10 mph limit through switch).
RED over RED	STOP	Stop. Do not proceed into next block except as permitted by [rule].

Items marked with "[rule]" indicate that there is (are) a rule(s) that may be invoked under specific circumstances for trains holding at signals displaying unfavorable aspects. These rules typically apply in situations where there are signal system problems and the position and movement of other trains is clearly understood.