REGISTER

This paper delivers a process of changing the signalling system of an operating railway (a brownfield resignalling project) whilst maintaining resilience during the difficult period of change (the transition period). Conventional resignalling projects have traditionally included a transition state. This would typically involve new signals being erected in advance of the changeover weekend and covered with a hood and a white cross, and pre-installing wiring at interfaces.

As signalling technology has moved onto the train, the changes required when replacing signalling technology have become more complicated. The number of players interacting with the signalling system has increased, and the commercial arrangements between those players has become more complex. The result of this is that the ability to change the whole system over one weekend has reduced.

There are only two solutions to this challenge: one solution is to introduce a significant closure of the whole system (typically three months or more); the alternative is to break the change into a number of steps, each of which is manageable over a weekend. This introduces temporary operating states (Transition States) between the current state and the final state but reduces the overall project transition risk.

This paper explains in further detail the need for such Transition States, and discusses the three different changeover methods. It concludes that change should be introduced in as few complex stages as possible, and that each stage should carry project risk that is just less than the maximum risk that the railway organisation is prepared to accept.