Power signalling, however, was installed in two signal boxes, one at the north and the other at the south of Doncaster Station. The work was planned and some equipment was on site before World War II but the installation was not commissioned until 1949. Searchlight colour light signals and electric point machines were controlled from switch panels. The interlocking equipment was unique being a sequence switch interlocking system manufactured by Standard Telephone Company using telephone switching techniques to the technical specification of the signal engineer of the then Southern Area of the London and North Eastern Railway. The sequence switches consisted of a rotary contact shaft which was rotated to a route position and proved a circuit through contact wipers. Each switch had a "home" position and eleven route positions. When a route was initiated, a clutch was engaged on the appropriate switch to rotate it into its correct position thus setting up the appropriate interlocking circuits through other switches and relays. The installations proved to be remarkably reliable, serving a very useful purpose but were eventually life expired.
In association with the resignalling scheme, was a major programme of track improvements to enable trains to run at speeds of up to 125mph. This was achieved by simplification and rationalisation of the track layout and realignment of curves at many places.
An early improvement was the adaptation of an existing railway bridge south of Doncaster to become a flyover enabling trains to and from the Lincoln line to cross over the main line without conflicting with the mainline trains.
The largest alteration to the track layout was in the Doncaster area where the work was staged over an extensive period.
The previous Marshgate Junction allowed for a maximum speed of 60mph on the Doncaster - York main lines with diverging speeds of 25mph on the main lines to and from Leeds and Thorne. Other speeds were 15mph. The remodelling of the layout in association with other improvements in the Doncaster station area allowed speeds of 105mph through the Doncaster section of the East Coast Main Line route. The divergence to and from the Leeds line allowed a maximum speed of 70mph. Other improvements on the Doncaster PSB area included raising the maximum permissible speed at Retford from 80 to 115mph and at Newark from 80 to 100mph.
Design of the scheme was governed by the need to satisfy operating requirements of speed and headway. Besides employing what was then modern signal equipment, an associated comprehensive communication network was necessary to achieve reliability and efficiency.
Track rationalisation and resignalling proceeded side-by-side, starting in the Grantham area and working progressively northwards while at the same time the new Doncaster signalling centre was constructed on a site south of the station and on the east side of the main line.
Dominating the control room is a 110 feet long illuminated signalling control panel, the wings of which are inclined towards the centre. On the near-vertical portion of the panel is depicted the track layout of the area controlled. Positioned on the layout to correspond with the location of all signals are push buttons which are used for operating points and clearing signals along the route selected for the passage of a train. Track circuits, which indicate the position of trains, are also shown on the diagram in distinctive colours.
Television monitor screens for two of the seven level crossings monitored by closed circuit television (CCTV) from Doncaster PSB, are inset into the panel itself (Kirton Lane & Rossington)and the other five are mounted on a separate desk console (Daw Lane, Arksey, and Moat Hills on the ECML; Bentley, and Dock Hills on the Leeds line).
Also on hand in the signal control room are read-out units for the special line side equipment, located at 16 sites, which detect over-heating in the axle boxes of vehicles on passing trains. If an abnormally high temperature is recorded the equipment will indicate the exact position in the train of the overheated axle and the signaller can have the train stopped and the vehicle examined.