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Dead medium: Train Token Signals System
From: jort@inetarena.com (Dan Howland)

Source(s): *Popular Science Mechanical Encyclopedia: How It Works* by Ellison Hawks (1941)

(((Dan Howland remarks: Train token signals were a system for preventing collisions on single sections of railroad track. As the text mentions, the baton and paper version was all but dead when the book was published in the early 1940's.)))

"Token Signals System

"The essential principle of the token system is that the engineer has in his possession a form of token that is visible evidence that the signalman has given him permission to travel over a specific length of track.

"In the earliest forms of this system, the token was a staff that resembled a policeman's baton, marked with the names of the stations at each end of the section.

"When two or more trains ran on a single line, the line was divided into sections, a staff being provided for each section. The staff for a particular section would be handed to the engineer at one signal box, and he would hand it in at the next box. From here it would be taken back to the first box by the engineer of the next train in the opposite direction, so that the staff was continually travelling between boxes.

"No engineer could enter the section unless he was in possession of the appropriate staff, and if this was not available, obviously there was a train already in the section whose engineer was carrying the staff."

(((Or the staff is sitting at the other station, and even though the track may very well be clear, you can't proceed. See below.)))

"This train staff system had a serious drawback, for where there were two successive trains in the same direction, with no intermediate train in the opposite direction, the staff could not be brought back to enable the second train to proceed.

"This difficulty was overcome by the use of the train staff and ticket system, in which printed tickets were used as the authority to proceed. The engineer of the first train was *shown* the staff, which indicated to him that a train could not be travelling in the reverse direction, as it was not carrying the appropriate staff.

"Having seen the staff, he was given a printed ticket, taken from a locked box. One such box was at each end of the section, and the staff to the section was the key to the box.

"The printing on the tickets usually was to the following effect: 'To the engineer. You are authorized, after seeing the train staff for the section, to proceed from station A to station B, and the train staff will follow.' The engineer of the last train of the series would take the staff and not a ticket."

(((I would argue that the represention by the baton of the idea that the track is clear, and the further abstraction of a printed chit representing the baton, makes this a "medium." Consider: if station A and B had a reliable, instant means of communication between them == say, you could simply see all the way down the line, or if the stations were within hollering distance == then there would be no need for the baton or the chit.)))

"Although this system is still in operation on unimportant branch lines, where traffic is light and fairly regular, there are possibilities of delays and inconvenience, and there is always the difficulty that the staff may be at one end of the section and the train waiting at the other end."

(((The solution to these difficulties was to have two machines which could issue keys, linked by telephone lines. A train traveling from station A to B had a key issued from station A. Until the train reached station B, it was impossible to issue a key from either machine.)))

(((bruces remarks: There are fascinating conceptual links here to telegraphy, flag signalling, and even token-ring computer networks, but let's face it: doesn't a telephone line render all this baton business irrelevant?)))

Dan Howland (jort@inetarena.com)
Journal of Ride Theory, P.O. Box 2044,
Portland, OR 97208-2044