Improving track, signalling and power

Track

When we talk about railway track, we mean the whole structure that trains run on, including:

1. Rails – these are the lengths of steel that are welded together
2. Sleepers – these are supports for the rails, and the ballast which is the stones beneath the track that provide support, drainage and ensure the rail’s alignment
3. Switches and crossings – these are moveable sections of track that guide trains from one track to another and allow them to cross paths. They have an especially limited lifespan because trains cause wear and deformation when they travel across them
4. Sets of points – these are mechanical systems that move the switches and crossings

As well as day to day maintenance, Network Rail invests in upgrades to support improving train performance and keep people moving for decades to come. For example, in 2018/2019 this included £67m of investment into the Brighton Main Line to tackle delay hotspots and boost the reliability of this key section of the network.

You can find out more about Network Rail’s work to maintain track at Network Rail.

Signalling

Signalling is what enables trains to move safely around the network. It’s essentially a sophisticated traffic light system for the railway. The complexities of moving trains around such a large network, keeping them safely apart, and allowing for their long stopping distances, means the signalling system is very complicated and comprises a great many parts.

The signals themselves are the lineside pieces of equipment that tell train drivers when it is safe to proceed and what route their train will take. In the future, the trend towards digital technology means that lineside signals will be replaced by in-cab displays. You can find this technology already in many of our trains.

The broader signalling system also includes systems for determining the position of trains, controlling the railway and operating the timetable, and points that control the directions trains take.

To keep everyone safe, signalling systems are designed to fail to a safe state, so faulty components can often result in signals remaining at red, causing train delays.

The signalling system is increasingly controlled from large rail operating centres, such as the centre located at Three Bridges which combines signalling control with the day to day management of the train service, everything from control over incidents through to social media, managed by a joint team from Southern, Thameslink, Great Northern, Gatwick Express and Network Rail.

At the moment we are working towards The Digital Railway. This is a strategy to modernise the railway involves the installation of cab signalling and sophisticated computerised and automatic train control systems. These will allow us to improve capacity and performance across the railway network, enabling more trains, better connections and greater reliability for our customers.

You can find out more about signalling at Network Rail.

Power

The majority of the Southern, Gatwick Express, Great Northern and Thameslink network is electrified, with a small number of diesel trains serving Uckfield and the Marshlink route to Ashford International.

The network uses third rail, predominantly in the south and overhead lines in the north. Many of our trains, such as the Class 700s on Thameslink and Class 717s on Great Northern can use both sources.

Third rail systems are always supplied from direct current electricity. Trains have metal contact blocks (‘contact shoes’) which make contact with the conductor rail. Conductor rails are mostly steel (a specially conductive type).

Conductor rails have to be interrupted at level crossings, crossovers (a pair of switches that connects two parallel rail tracks) and substation gaps. Tapered rails are provided at the ends of each section, to allow a smooth engagement of the train’s contact shoes.

The third rail is an inefficient conductor, so Network Rail has to provide a regular boost to the voltage every mile or so through substations. Network Rail is upgrading substations across the route to enable more trains to run. You can find out more about the third rail at Network Rail.

The second form of electrification on the route is through overhead line equipment (OLE), this is the name railway engineers give to the assembly of masts, gantries and wires found along electrified railways. All this steel and cable has only one purpose – to supply power to make electric trains move.

OLE supplies electricity at 25,000V, alternating current. By comparison to third rail, OLE is more efficient and enables trains to operate at higher speeds. The overhead wire carrying the power – the contact wire is supported by sets of masts, gantries and other supporting cables and is constantly balanced and held at the right tension. In turn, the contact wire transfers power to the train through a sprung structure on the roof of the moving trains called the pantograph – named for its resemblance to a mechanical drawing aid.

The OLE contains neutral sections, or “gaps” to isolate individual sections for maintenance or to separate sections of wire powered by different substations. When a train passes through a neutral section, a device called a vacuum circuit breaker (VCB) activates, isolating the train from the power supply. You can often hear this as a characteristic “thud” if sitting underneath the pantograph.

You can find out more about OLE at Network Rail.