David Reynolds
Chief Signalling Inspector, Network Rail
May 15 2006
Our second speaker of the 2006 programme was David Reynolds, Chief Signalling Inspector for Network Rail, who gave us an introduction to railway signalling.
He explained the development of signalling practice from the early days, where time-interval working kept trains apart and when people were employed to operate each set of points, through to today's modern computer-based control centres.
Modern signalling practice stems from the principal of the Absolute Block System, which only allows "one train into one block section on one line at one time". The section remains blocked to other trains until the train is proven to be out of the block, except where permissive working is authorised, e.g. trains are joined, split, locomotives changed, more carriages attached or where a failed train needs assistance. A signaller must learn some 53 standard bell codes as well as other local ones for routing purposes. Only a handful of lines in the country still use this type of operation.
Today track circuits give an indication of the train's location and whether a block is occupied or vacant. This involves a low voltage current being passed down a section of line – if a train is present the axles short-out the circuit. However, during the leaf-fall period a thick substance can build-up on the rails and cause problems for train detection. Axle-counters are a more modern solution and have been extensively used on the West Coast Route Modernisation, although these also come with their own set of problems.
In 1952 the first automatic crossing was installed on the York to Market Weighton line. Nowadays there are 7,674 level crossings in UK, with some 1,500 on public roads, and most are fully automated via track circuits. Barriers normally lower 27 seconds before an approaching train – the theory is that if motorists come to realise barriers come down too early, they'll be more inclined to weave around the barriers rather than waiting.
David concluded by talking about the development of powerboxes and integrated control centres, where signals are remotely controlled from central locations and far greater use is made of computer technology.
Written by Michael Pead.
Forthcoming Events
See the events list for more details on forthcoming events.