Railway Signalling

Train Operation by Signal Indication

was first put in use in the United States, 1882, at Louisville, Ky. Train movement was directed without the use of written train orders by signal indications given under the instructions of the dispatcher. In 1929 a large number of installations of train operation by signal indication without train orders were in use in the United States on single-track lines and for "either-direction" operation on multiple-track lines.

In 1927 an improved system was developed that further simpli fied the work of the train dispatcher and enabled him to increase substantially the output of transportation, especially on single track lines. The signals and switches of a district are operated and controlled from a central point by a dispatcher solely by the use of electric actuating devices and without the aid of operators. The dispatcher directs the movement of trains by operating the signals and by direct operation of the switches, also sets up the routes. (See Plate III., fig. 3.) Train Orders and signal indications differ greatly as a means for directing train movements. Train orders are written instructions that must be delivered to the conductor and engineman of the train. They must be correctly prepared, transmitted, delivered and understood. They must not be forgotten. On roads not equipped with modern signaling systems, safety of operation depends entirely upon the human element, for there is no check either electrical or mechanical to prevent an improper train move ment should an error occur in the preparation, transmittal or delivery of the order, or should the order be misunderstood or forgotten.

Signal Indications are simplified instructions for directing train movement given by the aspects of fixed wayside or cab signals. The train order calls for deferred action, whereas the signal indica tion, conveying instructions at the points where they are to be executed, calls for immediate action. Hence there is no lapse of time in which to forget the instructions.

Operation by train orders requires delivery of the order to the train. If in motion, the train must slacken speed or stop to receive the train order instructions as to how to proceed. As train orders are for the ultimate purpose of keeping trains moving, this slowing down or stopping for the delivery of orders in a measure defeats this purpose. Train orders when they retard the

movement of trains cause loss of time. To produce transporta tion, trains must be kept moving ; hence when train orders unnec essarily retard or stop the movement of trains, they tend to limit the production of transportation.

Train operation by signal indication on the contrary does not require the train to stop for proceed instructions and therefore tends to increase the production of transportation.

Classification Yards

located at important freight centres are for sorting and grouping cars for their respective destinations and for making up trains with the cars in destination order to ex pedite the road movement. These yards consist of a number of parallel tracks each assigned to a particular destination. The cars are sorted by switching them into these tracks. In flat or level yards, switch engines switch the cars. In modern yards, built on an inclined grade, hump or gravity type, cars are pushed to the top of the hump or incline and then move down by gravity into their respective tracks. Hand operated switches and switchmen have been replaced by power operated switches using either compressed air or electric motor-switch machines controlled by operators from central towers. These operators also control the power operated car retarders or track brakes which control the speed of cars moving by gravity into the classification tracks.

Prior to the use of car retarders, speed of the cars was controlled by hand brakes operated by car riders. (Pl. III., fig. 5.) Classification yards equipped with power switches and car retarders are worked at maximum capacity with minimum labour costs as switchmen and car riders are not required.

Highway Grade Crossing Signals

are for the protection of highway traffic crossing railway tracks at grades. The Interstate Commerce Commission lists for 1927 a total of 236,283 grade crossings in the United States: 12% of these crossings equipped with watchmen, gates or signals, 86% equipped with "railroad crossing" signs only and 2% not so equipped. The signals are largely of two types : a swinging disc and a red light or two flashing red lights.

The remarkable increase in motor-car traffic and the expanding net work of improved highways in the United States has made highway grade crossing protection a most pressing safety problem. (H. M. Se.)