What is... the Intercity Express Programme? (and what does it mean for the Great Western Main Line?)

The Intercity Express Programme is a £5.7 billion order for building the next generation of long-distance train in Britain. Or at least, that's the theory: its critics would claim it's an overpriced, wrong-headed solution in want of a problem to fix. It all started when someone decided many of our long-distance trains were getting a bit old. It's since morphed into something quite unusual, involving the first major use of electric-diesel "hybrid" trains (though it remains to be seen if that's actually a good idea)...

The High-Speed Train, or HST, also branded as the InterCity 125, entered service in 1977 and will probably still be in service for the rest of this decade. It was and is the mainstay of long-distance inter-city services across Britain; they regularly reach Penzance, Aberdeen, Sheffield, Swansea and many places in between.

They are diesel-powered, and are thus not used much on those routes which are already electrified; but they provide all long-distance services on the Great Western Main Line (GWML), as well as supplementing the fleets used on the Midland Main Line (MML), East Coast Main Line (ECML), and the Cross-Country routes. These days, they are easily distinguished by being one of the last fleets of trains with slam doors. But the HST was never designed to be around for so long; it was a stopgap solution.

As is so often the case, this stopgap solution ended up being a lasting feature of the British rail network. The plan in the 1970s had been for something much grander: the Advanced Passenger Train (APT). Capable of tilting round corners and hitting speeds in excess of 150mph, the APT was forged in the "white heat of the [technological] revolution" so championed a few years earlier by Harold Wilson. Unfortunately, it proved to be a bit too "white heat", and after many setbacks it was finally launched in 1981 while it was still prone to failures. The launch was a PR disaster, and only three production units were ever built, before being scrapped in 1985.

As a stopgap, the BR engineers had decided to build something a bit more conventional; and thus was born the HST. The fleet of nearly a hundred trains, with their distinctive angular power cars at each end, have served the country well for over 30 years now, but they are starting to show their age. While the typical lifespan of a diesel train is 25-30 years, the HSTs have all had their engines upgraded or replaced; nonetheless, asking them to go much past 40 years in service is pushing it.

So, in 2005, the Department for Transport set out to replace the HSTs. In a spectacular lack of ambition, they seemed only to want a like-for-like replacement; one high-speed diesel-powered train replaced by a slightly newer, slightly fancier, high-speed diesel-powered train. Fortunately, someone in the Department woke up to the opportunity that total replacement of the fleet could provide: since the trains need replacing anyway, why not make them electric? And indeed, once the investment in electrification was forthcoming, the need to replace the HSTs like-for-like evaporated.

Rather than scrap the "Intercity Express Programme" (IEP) and simply order some new electric trains to a standard design, the DfT pressed ahead with a revised plan for the IEP. There would be three types of train, all to be built to roughly the same design: electric trains, diesel trains, and "bi-mode" trains, the latter being hybrid trains capable of running off the overhead wires where there were wires, but also carrying underfloor diesel engines to take the train where the wires won't stretch. Eventually the diesel option was dropped, once the full plans for electrification emerged, but the bi-mode option was kept.

Ostensibly, the point of bi-mode trains is to be able to utilise the overhead wires between, say, London and Edinburgh, and then proceed on to Aberdeen or Inverness under diesel power. This means that you don't have diesel trains running "under the wires" for long distances, which ought to save on fuel consumption. But the key benefit of electric trains is that, almost uniquely among forms of transport, they don't have to carry around engines to generate movement. Bi-mode trains, though, mean still carrying around the heavy diesel engines even when you're not using them, and so one of the great benefits of electrification (lighter trains) is lost. It should result in an overall reduction in fuel consumption, but the jury is still out on that.

After a long and torturous bidding process, which was interrupted first by a review into the project's viability after electrification was announced, and then by the General Election and the Spending Review that followed, Hitachi were chosen as the preferred bidders, and would supply over a hundred Super Express trains. They will be built in Hitachi's new factory in Newton Aycliffe, Co. Durham, and marks the first major entrance of the Japanese train builders into the European market.

A total of 866 carriages, in a variety of 9-car and 5-car formations, some electric and some bi-mode, will replace all the HSTs on the Great Western Main Line (GWML) and the East Coast Main Line (ECML), as well as the Class 91 locomotives and Mark 4 carriages on the ECML.

I remain somewhat sceptical of IEP, especially the virtues of bi-mode trains: there are those who would have preferred a standard fleet of all-electric trains, and perhaps use diesel locomotives to haul them where there aren't wires, but I will reserve judgement until the trains actually arrive. It must be said, though, that however you spin it, £5.7 billion is a lot of money for this many trains; standard electric trains would almost certainly have been cheaper.

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Let's turn specifically to their impact on the Great Western Main Line. Combined with electrification, the new trains ought to bring a step change in performance and journey times; but on their own they cannot on their own provide the necessary capacity increase on the GWML.

London to Reading is perhaps the single busiest passenger flow on the whole railway network, with commuters flooding long-distance trains for the non-stop run to London, and making it near-impossible to get a seat in rush hours. If there is to be enough capacity to provide a meaningful increase in seats in the peaks, more has to be done. Fortunately, more is being done. For one, Crossrail's arrival in 2019 will free up a significant number of platforms at London Paddington, meaning they can be used by longer-distance trains instead.

But Paddington isn't the linchpin of the GWML: the biggest bottleneck, by a long way, is Reading. Reading has long suffered from not having enough platforms - fast trains out of London in particular had only one platform available - and too many conflicting routes, with freight trains between Southampton and the north having to cross the main GWML, and with Cross-Country services added to the mix there was never enough capacity. Here's Reading as it looked in 2009 (click to expand):

Reading station layout, 2009

Fortunately, for the last five years Reading station has been undergoing one of the biggest rebuilding and remodelling projects ever undertaken on the British railway network. In a £900 million scheme, five new platforms have been added, and two viaducts to the west end of the station will open next year to segregate east-west traffic from north-south traffic. The scheme, due for completion at Easter 2015, will dramatically increase capacity through Reading, permitting fast trains to run as often as every three minutes between London and Reading. Here's Reading as it will look in 2015 (click to expand):

Reading station layout, 2015

As you can see, the layout of the railway will be transformed. One of the most innovative features is the "Reading Festival Chord" (in light green above), a roller-coaster of a track that goes under the main lines and then over the "feeder" lines from Reading West. What it means is that Cross-Country trains between Birmingham, Oxford and Southampton will be able to reverse at Reading station without ever having to cross the path of high-speed services on the GWML, and that is nothing short of genius on the part of the designers of the scheme.

There is one last part of the puzzle for the GWML, and that is the question of what trains will provide suburban services into and out of Paddington. While Crossrail will take over the stopping services, and the Hitachi Super Express trains (from IEP) will provide the long-distance services, a fleet of electric units will be required for the semi-fast services to Oxford and Newbury, as well as for the branch lines to Windsor, Marlow, Henley and Basingstoke (which will also be electrified).

Here comes the clever part: by syncing up the electrification of the GWML with the Thameslink Programme, no trains need be built specifically for the GWML suburban services; instead, trains will simply transfer from Thameslink over to the GWML. Initially, those were planned to be the Class 319s that currently run on Thameslink, but instead the newly-built Class 387s - which are capable of 110mph, rather than just 100mph - may be transferred; that has yet to be decided.

All told, the Great Western Main Line will be transformed by 2019:

• 650 track-miles of electrification;
• brand-new Hitachi Super Express long-distance trains running between London, Bristol and Swansea;
• electric suburban trains providing fast commuter services from Oxford and Newbury;
• Crossrail services providing through trains from Reading and west London to the City;
• five new platforms and a completely new layout at Reading.

This will enable a "very high frequency" timetable to be introduced - with three or four trains an hour between London and Bristol, compared to just two per hour currently - which should bring a completely different experience to the GWML, just as the very high frequency timetable introduced on the WCML in 2008 has meant I can get from Coventry to London in an hour (a distance of 94 miles), and if I miss a train I only have to wait 20 minutes.

On top of that, following on from the electrification of the GWML, it is planned to electrify the South Wales Valley Lines, a dense network of suburban routes into Cardiff: another 200 miles of track should be electrified by 2020, bringing electric suburban trains to Cardiff and revolutionising rail travel in South Wales - though the details have yet to be worked out.

With all that said, I should point out that not all of the Great Western Main Line will benefit from these upgrades. The electrification will not extend to Gloucester, Cheltenham, Worcester or Hereford; but they will at least benefit from bi-mode trains, capable of running of the electric wires as far as Swindon or Oxford. More importantly, the overhead wires will not go south of Bristol or west of Newbury - meaning all of Devon and Cornwall will remain unelectrified, and indeed will still be served by (refurbished) HSTs, if current plans are anything to go by.

So while parts of the Great Western network flourish, Devon and Cornwall may feel like they're stuck in stagnation. With this kind of scheme, though, there are always winners and losers; in this case it's clear that Bristol, Cardiff, Oxford and the like will benefit from significantly improved journeys to London. And while Devon and Cornwall will not see so much investment immediately, that doesn't rule out the possibility of extensions to the electrification later; indeed, I'd count on at least one major extension to the GWML electrification before 2025.

The Great Western Main Line is going through a momentous phase in its history, perhaps the biggest change since the days of Brunel. It remains to be seen exactly what emerges in 2019, but it's clear there will be faster, more frequent trains - at least for some.

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