Hand Signals
Between 1838 and 1841 hand signals were used. They worked well enough as long as trains were slow and stopped at all stations. Trains in this era used hand breaks (brakes) to stop. At 40 MPH stopping could take half a mile, at 60 MPH a mile to a mile and a quarter. A man standing on the ground simply could not be seen within stopping distance at over 40 MPH. The solution was the Disk and Crossbar Signal.
A four foot diameter disk facing the
driver told him the track was clear at least as far as the Railway Policeman
(Signalman) could see, and the last train had been out of sight for the
prescribed Time Interval.
An eight foot long crossbar showed
Danger ahead (Stop).
The right most crossbar
applies to the Down line only. The centre crossbar applies to the Up line
only and the left most crossbar applies to both. Up lines carry trains to
London. Down lines carry trains away from London. The pole might be up to
60 feet tall in order to be seen over obstructions.
Caution
A third signal could be shown using a separate fantailed board.
By turning the fantail the opposite the to show the red side repeated the Danger Signal which might be difficult to see near the pole.
The edge of the fantail turned to the driver meant the line was clear.
At this time:
Red signaled Danger.
Green signaled Caution
White Signaled Clear.
Junctions were protected by a double disk and crossbar. A double bar was an unambiguous signal to stop. A driver seeing a double disk hoped the signalman was certain who was next on the schedule, otherwise the signal might show clear for the wrong branch of the junction.