Resignalling the Underground

Customers of the Northern line – London Underground’s busiest – are set to benefit from 20% more capacity and almost 20% faster journeys next month thanks to a new signalling system, writes David Waboso.

 A new signalling system was commissioned earlier this year (ahead of time and budget), and with the introduction of an increased timetable, customers will see the benefits from 14 December.

But how does signalling achieve this? I spend a lot of my time explaining this to people – because, despite the substantial benefits of replacing signalling systems, to the average customer it is very much unseen and behind the scenes, only visible when it causes delays.

How does it work?

Signalling is the core of any high capacity rail system. It’s the overarching safety and control system for train movements. It responds to the demands of the timetable and allows trains to run closer together, in safety, at higher speeds – maximising the capacity you can get out of fixed infrastructure.

The Northern line joins an increasing part of our network where capacity has been dramatically improved with new signalling and in 2011, we completed the re-signalling of the Jubilee line, providing 33% more capacity, more frequent trains – now 30 every hour, and overall carrying 12,500 extra passengers an hour on a service that’s 50% more reliable. The Victoria line, upgraded in 2012, is even more frequent, now delivering a capacity of 34 trains per hour, the highest in Europe as well as record levels of reliability.

On the Tube network, we have been implementing this through CBTC (Communication Based Train Control) systems. CBTC is offered by all major signalling suppliers (which is not a large number) and is comprised of computerised sub-systems on trains, wayside, and  a central control “brain” talking to each other in a complex network. The system effectively controls trains between stations, and reports each train’s position, destination and speed. The central computer is the ‘controlling mind’ for this and determines how we can run the maximum number of trains.

It’s highly challenging  to implement this type of a new system – especially on operational lines, and because modern signalling comprises hardware and software written with safety critical code it requires a thorough and thus lengthy safety sign off process (rightly so, since some of these lines carry close to a million passengers a day).

As well as ensuring safety, we need our service to be reliable and any implementation programme requires significant access to trains, track and equipment rooms for installation and testing. On a busy railway, providing such access is another challenge

These are not issues unique to the Tube. Mainline railways also run reliable and frequent train services and are investing in similar technology (European Rail Traffic Management System or ERTMS) and the challenge of upgrading on busy operational lines is the same.

A long history of innovation in signalling

Our investment in state-of-the-art signalling didn’t just start with the Jubilee line a few years ago. We actually first started this in 1967 when LU introduced the world’s first automatic railway on the Victoria line. Automatic railways were then developed and propagated worldwide, with systems implemented in places like Hong Kong and Singapore.

Here in London, automatic signalling came back full circle when the ‘grandchild’ of the Victoria system was installed on the Central line in the early 1990s. This system has enabled capacity today of over 30tph through the heart of London. On the second busiest line on our network, we could frankly do with even higher frequencies.

In 1987, we opened the Docklands Light Railway (DLR) in east London – a fully automatic/driverless system. It was later re-signalled with North American ‘moving block’ technology, triggering a move by other metros to similar systems.

The DLR system was developed for application on the Jubilee and Northern lines. And a further descendant of the Central line signalling system was installed on the Victoria line. I mentioned earlier we now run up to 34 trains per hour on the Victoria line – one of the highest frequencies in Europe. When I’m catching a Victoria line train, I marvel at how quickly trains come in, clear the platform and leave again. If you stand at the headwall, you can literally see the lights of the next Vic line train coming down the tunnel.

Automated efficiency

CBTC systems have allowed us to increase capacity of our existing infrastructure by up to 30%. Yes, it’s challenging work applying complicated systems to an already busy network – in fact upgrading our lines to automatic signalling systems has demanded the highest levels of project management, engineering, operations and maintenance. But the result is that we’ve been able to meet the ever-increasing demands on our system without having to build expensive new infrastructure. This points the way for how we’ll deal with increased demand on the Piccadilly line and Sub-surface railway (Circle, District, Hammersmith & City and Metropolitan lines) in the next few years.  

David Waboso is capital programmes director for London Underground