Electrifying Our Railways

A Class 395 Hitachi “Javelin” stands at Ashford International Station.This train is dual-mode, able to draw power both from the third rail, visible in the foreground, and the Overhead Line Equipment (OLE) visible above the train.
Class 395 ‘Javelin’ at Ashford International – photo by TheFrog001, Creative Commons Zero, Public Domain Dedication

Our railway network needs to be electrified if the UK is to meet its net-zero carbon pledges. Rail has a carbon advantage over road haulage – producing 76% less carbon even when using diesel trains. This really means electrifying the whole network.

The map shows where the railway is already using electricity in Britain. About 38% of our railways are electrified – although the programme is continuing on a stop-go basis. About 30% of the electrified part uses a third rail DC input.

That part of the network is in London and the South-East (seen in green on the map). This electrification work was mostly done in the interwar years, although some was done earlier around Merseyside.

Power Supply

Third rail means that an extra rail is electrified with a DC current. This poses a greater risk of electrocution of those who get on the lines in comparison with overhead electric lines which, pose less risk. In 1956, British Rail decided that all new electric lines would be overhead, running at 25kV AC. (These are the lines running north, red on the map).

There is a good  reason for that decision. Although there are five different standards in Europe, the Treaty of Rome specified that the international network should be integrated and the TGV lines in France operate on this 25kV standard.

Indeed it has become a world standard for high speed lines – including those in the US and Japan and other places in the Far East. These 25kV AC systems all use overhead wires which are safer.  

HS1 from the Channel Tunnel to London St Pancras also runs on 25kV AC with overhead lines (as shown in the picture of a train at Ashford Station above). HS1 was constructed to the same loading gauge as the high speed lines of Continental Europe so that the same locomotive could run right through Kent from London to Paris or Brussels.


Although this is the same track gauge as in the rest of the UK, in fact the size of trains in Continental Europe is larger, which means that bridges and tunnels need to be replaced in the North of England. The good news is that our freight trains can travel through Europe, but theirs can’t come through Britain.

The advantage of using this continental (now universal) electrification standard is that the trains run on a faster speed (up to 400 km/h), and the rail stock is cheaper, as greater volumes are manufactured than for trains made for specific national gauges.

DC Outmoded?

The DC mode with a third rail used in London and the South East and Merseyside was mostly built between the first and second world wars. Electric trains made sense in the suburban context since they needed to go through many tunnels and pollution would have been a major problem.

The London Underground operates on a 630V DC fourth rail system, and interestingly the Docklands light railway also has a third rail but at 750V DC. It also has plenty of insulating material to prevent human electrocution – both for people trespassing on the lines and staff maintaining the system.

The routes in the former Southern Region use a slightly different third rail system from the London underground as it runs at 750V DC. 

Speed Limit 80

The problem for the government’s electrification programme is that this doesn’t allow the trains to run faster than 80mph and rather too much heat is generated. The most modern trains in the south east use a regenerative braking system which dissipates the heat and sends energy back to the train.

Transport Scotland has also developed more electrified railways between and around the main cities. It is somewhat curious that the new name for Network Rail is to be GB Rail, when Transport Scotland is already devolved.

AC/DC What’s the Difference?

We now need some clarification of the advantages and disadvantages of AC (alternating current) and DC (direct current). AC is what we use every day in our homes when we plug into the wall socket. It is also used for the electricity cables covering the national grid. However batteries generate DC – eg for electric cars and computers.

Some loss occurs when transporting electricity over long distances and some have suggested that the loss would be less if DC were used (eg to transport electricity generated from solar panels in the Sahara to Europe). There is also some loss every time electricity is converted from DC to AC using an inverter and vice versa.

Seeking Greener Generation Of Electricity

Having said that, we must decarbonise the railways: if they use electricity, that needs to be generated from green sources. Solar power is unlikely to supply the power that is necessary (and it is intermittent). There has been much discussion about using batteries and solar panels in the rail industry but whereas these might be usable for stations, carrying batteries on trains might not be practical.

Is Hydrogen an Alternative?

That also applies to using hydrogen – which also involves a battery. Research at Birmingham University has tested a hydrogen powered system which can be fitted underneath existing trains.

On one of the government’s halting of the electrification programme, they suggested using biodiesel, but bringing that into manufacture may take longer than continuing with the current electrification programme.

Now You See It, Now You Don’t

The Western side of the UK is mostly not electrified, although there have been plans put forward and then cancelled across recent decades. So where there is no electrification, trains are pulled by diesel engines, which are smelly and noisy.

There are some parts of the rail network in the UK where there are gaps between the electrified parts (eg between Didcot and Oxford). Here they use bimodal trains with the electric pantograph on top of the carriages which can hook onto the catenerary when there is electricity, but use diesel engines when not.

“GB Rail” Is Barking Up the Wrong Tree

More and more of these engines are likely to be bought for the British system as GB rail plans to run trains both on the main spines and then on to unelectrified lines. But a risk that hit the news recently was finding that air pollution inside the carriages was worse on these bimodal trains (as found in the London to Bristol trains).

Our Rails Cost Twice As Much

One of the advantages of choosing a world standard for railway electrification is that we can compare costs with other countries. An analysis of 20 electrification projects in Britain and mainland Europe found almost half of projects achieved a cost ranging from £750,000 to £1m per single track kilometre (stk).

However, almost all the most recent electrification projects recently completed  by Network Rail have cost over £2million (stk). In particular the government took fright over the cost of the Great Western project from Reading to Cardiff.

Staff Retention Is a Problem

One of the problems with the stop-go method of financing rail projects is that if there is no work for the engineers, they tend to disappear and it is difficult to get this expertise back again.

The RIA (Rail Industry Association) recommends establishing a 10-year rolling electrification programme “to progressively lower the long-term operating costs of the railway towards European norms and support investment in people, process and plant.”

The report also urges the adoption of proven systems that comply with relevant standards, and a review of Network Rail standards and risk allocation.

“We Apologise For the Late Arrival…”

Last July,  the Department for Transport agreed to publish details of the rail electrification programme “shortly” in order to meet its commitment to decarbonising the UK’s transport systems. However, we’re still waiting for its publication after nearly five months.

New data published by the ORR (Office of Rail and Road) shows that the UK is not electrifying its railways quickly enough to meet Net Zero by 2050.