Borough Market Junction was a traffic bottleneck. Six running lines flowed from London Bridge and diverged into four lines for Cannon Street and two for Waterloo East and Charing Cross. The core of the problem was the conflict of trains heading into Cannon Street and out of Charing Cross. In the early 1960s the demise of steam seemed to offer a window of opportunity to increase the flow of trains over this crowded junction and resolve these conflicting moves.
Using steam locomotives generated many light engine movements; as engines ran round their trains, shunted carriages and went to coal, water and turn round. Replace steam with electric multiple units and at a stroke, you create new train paths; paths that could be used to strengthen peak services. With a change of terminal destination departures at key moments; so Charing Cross trains did not conflict with Cannon Street services, Borough Market Junction could handle even more passenger trains.
Now could engineers make train operation even more efficient at Borough Market Junction, by replacing its human signallers with a computer system? Could the white heat of 1960’s computer technology transform Britain’s busiest Signal box? In short, no; after 18 months investigation the Divisional Engineer declared ‘no computer so far devised could be programmed so as to replace in rapid and alert action the skill of the signalmen at Borough Market Junction.’