You can not forget extras. Usually white was the marker of a second section of a train. The front markers on the locomotive would be green indicating a following section and the rear marker would be white on the first and second but green on the last section. Company rule books would indicate what color for what lamp of each train. Remember it is not a train until it displays markers. Until then its just a bunch of equipment joined together. This is from a 1959 PRR book of rules after front markers were removed.
19. The following signals will be displayed, one on each side of the rear of every train, as markers, to indicate the rear of the train:
By day, on cars not equipped with fixed electric marker lamps, marker lamps not lighted; on engines and cars equipped with fixed electric marker lamps, marker lamps lighted as at night.
By night, on engines and cars, marker lamps lighted showing red to the rear except in manual block signal system territory when clear of main track, marker lamps lighted showing yellow to the rear.
A train not equipped to display markers will display on rear of train, by day, a red flag; by night, a red light except in manual block signal system territory when clear of main track, a white light.
When cars are pushed by an engine (except when shifting or making up trains in yards) a white light must be displayed on the front of the leading car by night.
When an engine is running backward without cars or at the front of a train pulling cars, a white light must be displayed by night on the front of the movement if not equipped with a headlight.
25. Each car of a passenger train, when practicable, will be connected with the engine by a communicating signal appliance.
When emergency repair work is to be done under or about cars in a train and a blue signal is not available, the engineman will be notified and protection must be given those engaged in making the repairs.
When a blue signal is placed at one or both ends of an engine or cars to which an engine is attached, the engineman must be notified; he must also be notified when the blue signal is removed. (Rev. 2-27-59)
When emergency repair work is to be done under or about cars in a train and a blue signal is not available, the engineman will be notified and protection must be given those engaged in making the repairs.
When a blue signal is placed at one or both ends of an engine or cars to which an engine is attached, the engineman must be notified; he must also be notified when the blue signal is removed. (Rev. 2-27-59)
Also from the same book.
Train--An engine or more than one engine coupled, with or without cars, displaying markers.
Extra Train--A train not authorized by a time-table schedule. It must be designated as:
- Extra--for any extra train except passenger train extra or work train extra.
- Passenger Extra--for passenger train extra.
- Work Extra--for work train extra.
Regular train--A train authorized by a time-table schedule.
Superior Train--A train having precedence over another train.
Train of Superior Right--A train given precedence by train order.
Train of Superior Class--A train given precedence by time-table.
Train of Superior Direction--A train given precedence in the direction specified by time-table as between opposing trains of the same class.
To be really confused look at this rule book. Starting on page 22. Train signals.
