the rail engineer • May 2013
under a tripartite agreement. Just one rack of electronic modules replaced a large room full of relays. The first SSI installation was commissioned at Leamington Spa in 1985, controlled from an NX panel. Over time, SSI has proved to be highly successful, being deployed extensively on the national network with considerable export sales. Storm clouds gathered over SSI when Railtrack took over the infrastructure. SSI was perceived as outmoded - ‘old BR’. The future was with the Computer Based Interlocking (CBI - generic term). Actually, SSI is a CBI, but SSI was apparently dead in the water. The new CBI kids on the block were GETS with the ‘VHLC’ for Norwich to Cromer, Ansaldo STS with ‘ACC’ for Manchester South, Siemens with ‘SIMIS-W’ for Dorset Coast, and Adtranz (now Bombardier) with EBILock for Horsham. The introduction of this new technology provided major challenges at product acceptance. It was difficult to demonstrate that such products would work safely within the parameters of UK signalling principles, for which they were not originally designed. This was to cause significant cost over-runs and delays to projects. There was some
unfortunate de-scoping in order to restrain the budget. At Stockport, lever frames which date from the nineteenth century still control the station area! Dorset Coast became just Bournemouth. The Horsham project was abandoned altogether. However, some success was achieved with follow on contracts for the GETS ‘VHLC’, Ansaldo STS, ‘SEI’ at Machynlleth, and Siemens ‘SIMIS-W’ at Havant. With Network Rail at the helm, there was a dramatic reversal of policy. SSI was firmly back on the agenda and is again being extensively installed around the network. This has encouraged innovative new SSI compatible
products such as Invensys ‘WESTLOCK’ and Alstom ‘Smartlock’. These workstation and interlocking products will continue to provide for the safe passage of trains for many years to come within the operating environment of the new ROCs. Overlay sub systems will be added to the ROCs as required such as Automatic Route Setting (ARS), strategic train regulation, and ETCS (cab signalling).
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