The New Zealand Railways Magazine, Volume 3, Issue 2 (June 1, 1928)
Great enterprise has been displayed by railways the world over in recent times in the development of automatic signalling installations. With the speeding-up of train schedules and the dense traffic handled on main lines, automatic signalling has to-day become a necessity on many routes, and here at Home increasing employment of automatic signalling devices is a feature of railway activity.
By the London, Midland and Scottish line—England's biggest railway undertaking—there has just been installed automatic signalling of a most efficient type on one of the most difficult stretches of track in the London area. This is the Bow Road and Barking route, over which there is conducted a heavy electric passenger service and a heavy steam freight service in connection with the movement of traffic between the London docks and northern centres. The new equipment has rendered possible a saving of six minutes on the passenger train timing between Bow Road and Barking, and the installation includes 43 new signals and 41 fog repeater signals, as well as 74 new track circuits.
Over the tracks in question there are now run forty passenger trains per hour in each direction. To ensure safe working, much shorter spacing between signals has been allowed, this being made possible by the high braking power of the electric trains and by utilising to the fullest degree the gradients existing along the route. Freight train working along the section is conducted principally during the night time, all trains being steam operated. The freight trains have not the braking power of the electrically operated passenger trains, and a system had to be devised allowing a greater distance between the freight train and the next train in advance than was called for under purely passenger train working conditions. To admit of this there has been installed a special instrument providing automatically for the extra distance required, the passage of a freight train automatically restoring the track to its normal working so that no delay is suffered by following electric passenger trains.