Singling of Double Track Lines

Abstract

THE Great Southern Railways of Ireland have singled 220 miles of double track railway, that is, trains can travel in both directions along each track. It has been found that many of these double track lines which have never been worked to full traffic capacity can be operated as single tracks with little or no reduction from the flow of full traffic. This method of working has led to a very special and improved method of signalling which is described in a paper by Mr. H. Birchenhough, read to the London Students' Section of the Institution of Electrical Engineers on November 27. Permission to occupy a section of the lino is given to the driver of the train by means of a token which he carries through the section. In Great Britain, tablets, staffs and keys are used as tokens, but the ball token is often used elsewhere. Every single track section equipped for token operation has installed at each end of the section a token instrument containing a supply of tokens. By means of a wire the two instruments are electrically connected and so interlocked that only one token at a time can be inserted, thus ensuring absolute safety. The tokens used in adjacent sections are of different type, and this provides an additional safeguard. When single line sections have outlying sidings or branch lines into which trains can be moved, it is sometimes necessary, and during operation it may be desirable, to clear the section for traffic; in this case a subsidiary instrument is placed at the siding into which the section token can be placed after the section has been cleared and the siding points reset for the main line.