Moving Block Signalling

Network Rail is developing a programme for the national roll-out of the European Rail Traffic Management System (ERTMS), using European Train Control System (ETCS) Level 2 signalling technology, within 25 years. It is also undertaking work to determine whether ETCS Level 3 technology could be used to speed up the deployment of ERTMS to within 15 years.

Implementing ERTMS with ETCS Level 3 has the potential to increase railway route capacity and flexibility, and to reduce both capital and operating costs. It would also make it possible to manage rail traffic using a moving block signalling approach.

In moving block signalling, trains are given permission to move to a specific position anywhere on the track, as defined by a computer system. This is in contrast to the fixed block signalling used on the vast majority of Britain’s railway (in which trains are granted permission to move to a pre-defined, fixed position – i.e. the next signal).

Moving block signalling effectively maintains a safe ‘envelope’ of empty track around each train, which moves with that train. This envelope can be tailored to match the breaking performance and speed of that specific train, optimising line capacity in different situations. For example, the same track could be used to run lower-speed commuter trains (with shorter stopping distances) closer together, and high-speed trains (with longer stopping distances) further apart.

Although moving block signalling can increase the capacity of railway routes compared to fixed block signalling, in practice there are still constraints, largely due to train braking performance and timetabling restrictions. This means that the increase in capacity provided by moving block signalling differs between routes.

Research in this area is conducted by a range of organizations from across industry, academia and Government. Not all of the results of that work are publically available. This briefing draws on information from interviews with experts from academia and industry, and a sample of the publically available literature.