Ath of NR’s Digital Railway

Carne did give some ground on one of NR’s more controversial claims - the claim that Digital Railway will bring a 40% increase in capacity. He stood by the claim for dense commuter lines, but admitted that DR wouldn’t deliver this on long-distance routes.

Squeezing more trains onto a line needs shorter gaps between them. This demands more accurate information about their location. Conventional signalling can do this by erecting more signals and installing more track circuits or axle counters. These circuits and counters determine a train’s position and allow signalling systems to more accurately place trains. At Level 2, ETCS does away with the signals but it still needs the circuits or counters. Simply switching signals for a screen in the cab does not improve capacity.

Level 3 removes the need for circuits or counters because the train itself works out its position and sends this via radio to the control centre. This allows for ‘moving block’ (as opposed to the fixed block created by track circuits). The signalling then computes the best distance between trains depending on their speed (just as car drivers do - nose-to-tail in crawling traffic, longer gaps at higher speeds). Signalling company Thales reckons ETCS L3 is ten years away from widespread deployment.

In any case, signalling experts will point out that capacity is not limited by the distance between trains on plain track. More constraints come from the mix of fast and slow trains, their stopping patterns, and the capacity of termini to receive and dispatch trains.

Termini challenge ERTMS, especially its GSM-R radio system, which is based on ageing technology (akin to 2G in mobile phone terms). This means that it does not have capacity to cope with the number of trains in a busy station. Upgrading it to GPRS will help, and this forms part of NR’s plan.

Elsewhere in Europe, railways swerve around this problem by retaining conventional signalling at busy termini, which negates any capacity benefit ETCS might deliver elsewhere. It shows that Europe sees ETCS installation simply as a signalling renewal, whereas NR sees it as a much wider project.

There are further problems with GSM-R. GPRS is now old technology and will be obsolete in a decade. Even today, commercial mobile phone networks interfere with it. That’s why a 3G transmitter in Cardiff is switched off because it interfered with railway communications.

The railway radio of the future must have sufficient capacity and must not be susceptible to interference from other networks, because that would be another source of delays to trains. The UIC has just issued the specification for a future rail radio system. Yet, as NR’s Chief Digital Railway Engineer Andrew Simmons told MPs, this specification is likely to take two to three years of discussion before plans can be further developed.

Part of NR’s problem is that its tracks are crowded and busy now. In the rest of Continental Europe, there’s less pressure for technology to solve congestion and less impetus to move forward.

There are hints that signalling manufacturers are in little hurry to move towards ETCS L3 because they want to recoup their investment in L2. Meanwhile, the European Railway Agency would like to see L2 being used successfully before moving to L3, according to the Institute of Railway Signal Engineers. This gives NR and Britain an opportunity to lead L3’s development, but also the challenge of dragging European railways along a road they don’t yet wish to travel.

In the meantime, passenger numbers in Britain keep rising. As Carne admits, DR is not a panacea, and major projects such as High Speed 2, Crossrail and Crossrail 2 are needed in addition to smaller improvements. But he’s in a hurry to deliver his vision of a better railway. “150,000 people a day are standing on commuter trains - we have to do something, and we have to do something fast,” he told MPs.

Is it churlish to suggest that if he finds seats for those 150,000, their floorspace will simply be taken by another few hundred thousand standees? Philip Haigh is a former deputy editor who is now a freelance writer specialising in railways. He is an associate member of the Institution of Mechanical Engineers. You can contact him via thorpestreetmedia.com and follow him on twitter at @philatrail