On April 3, 2007, a sleek train raced across the countryside of northeast France, pursued by a small jet aircraft. On an open stretch of track between Prény and Bezannes, the train galloped ahead – eventually reaching 500kph. Officially, no train operated by TGV, the French state-owned high speed service, had ever ever surpassed 515kph, the speed record set by the same firm 17 years earlier. This attempt, christened Operation TGV 150, was aiming to reach 150 metres per second, or 540kph. As the chase aircraft beamed data and video to pensive engineers, the train pushed beyond 540kph, before setting a new world speed record: 574.8kph.
Since then the world has seen a boom in high-speed rail. In 2011, the EU set out to triple the length of the European network by 2030, and since 2000 has invested €23.7bn (£20.42bn) in the development of high-speed rail infrastructure. In the last ten years alone, the number of passenger-kilometres travelled annually on high-speed trains (those operating at speeds over 250kph) has increased 350 per cent, to 845 billion. The lion’s share of this growth has taken place in China. Since the country inaugurated its first high speed service, a 120 km route between Beijing and Tianjin, in 2008, it has built over 20,000km of track, served by 1,200 trains.
With air travel under increasing scrutiny as a dangerously indulgent mode of transport, rail is often touted as the greenest form of mass transit available. Across Europe and Asia, ultra-fast trains are racing to capture overland routes back from the air industry. Can high speed rail make long distance travel green again?
“The big issue is power,” says Alan Vardy, emeritus professor of engineering at the University of Dundee. “The power required increases with the cube of the train speed.” That makes squeezing each additional boost in speed exponentially more difficult – and expensive. “You’ve got to have the electricity to provide that power, and the motors of the vehicle have to cope with that power,” he says.
Typically, that power (around 15,000 to 25,000 volts worth) is supplied by catenaries, overhead wires that a train contacts to via a raised arm called a pantograph. These wires are not rigid, but draped between support pillars. “As the train goes under, it distorts the shape of wire, and the whole thing shifts,” says Vardy. The faster they go, the more the wire sways. “There is a fair amount of technology just keeping the pantograph in reasonable contact with the wire.”
And as trains get faster, increasing that speed becomes even harder. Air resistance become a major factor with increased speeds. “Double the speed leads to four times as much loss to drag,” says Hugh Hunt, researcher in engineering at Cambridge. “So high speed trains have really sharp pointy noses.” The famously long noses of Japan’s Shinkansen ‘bullet’ trains are actually there for a different purpose, however: preventing sonic booms. As a train enters a tunnel, it acts like a piston, creating a shockwave that races ahead of the train. The aerodynamics of long, narrow tunnels can result in a cacophonous bang at the far end – to the irritation of those living within earshot.
The problem is particularly acute in Japan, where tunnels were built before the effect was understood. Engineers designed trains with elongated nose cones to soften the sudden increase in air pressure. High-speed trains in Europe go just as fast as Japanese bullet trains – if not faster – but the phenomenon is rarer due to larger bore tunnels. Where it does occur, engineers usually tackle the problem by adding a long hood to the tunnel. “Just like the long nose makes is possible to operate in tunnels without any hood, the hood makes it possible to operate without a nose cone,” explains Vardy.
Sudden pressure changes in tunnels are also uncomfortable for passengers, and for this reason all high-speed trains are pressurised to some degree. But this creates a new problem: the pressure difference has to be shouldered by the chassis of the train, and over time, leads to fatigue issues.
At high speeds, noise also becomes a big issue. Narrow tunnels are also a problem in the UK, where they were built for smaller nineteenth century vehicles, and limit the amount of noise insulation that can be added to a modern train. Noise increases with speed, and high-speed trains are usually fitted with skirts to muffle the shriek of steel wheels on steel track. This sound is especially bad if the rail isn’t constantly ground down. “High speed tracks have got to be very, very smooth,” says Vardy. “You can hear it if you go on the Underground in London, or any city, sometimes it becomes really noisy because that section of track has become corrugated.”
At 400kph, high speed transport is a moving experience for more than just the passengers. The speed of a train is dictated by the rail it runs on, which is set down in stone – literally – when the track is laid. The sharpness of curves – as well as the tilt they are given, to allow the train to lean into the turn – sets a cap on the maximum speed a train can pass it safely. Tilting trains can squeeze a little extra speed from existing track, but then any existing track must be redesigned or replaced with purpose built high speed line. Costing around $30m (£23m) per kilometre, this soon adds up.
Even the ground below the rail can be affected by the rumble of trains. “There are problems of liquefaction,” says Hunt. “In Belgium, quite a lot of the reclaimed land is quite soft soil, it has to be stiffened for high speed trains.”
Assuming we’re willing to supply a custom-built track – and pay for the constant maintenance required – how fast could a train go? “We consider theoretical maximum speed to be about 600kph,” says Laurent Jarsalé, vice president of the High Speed Product Line at French rail giant Alstom. The hard cap is set by the copper catenary that supplies the train with power: as speed increases, the cable must be held in ever-higher tension. But there is a limit to how tightly you can lace this copper wire before it snaps.
Yet it’s unlikely you’ll be able to ride a train running at half the speed of sound any time soon – or perhaps ever. The fastest non-levitating train currently in service is China Railway’s Fùxīng Hào, which hits 400kph between Shanghai and Beijing. This will be rivalled when Japan’s new fleet of ALFA-X bullet trains arrives in 2030, boasting comparable top speeds.
Most of the time though, both will be travelling much slower than that, around 350kph. “There’s a big gap between the maximum record speed, and speed which is considered optimum for everyday operation,” says Jarsalé. “The market is not looking for these kinds of very high speeds. We need to find the technical-economical optimum, that is most often defined to be around 320kph.”
“The key thing is journey time, not speed,” says Mark Smith, the ex-railway manager better known as The Man In Seat 61, after his travel website of the same name. The standard rule within the industry was that rail competed best against air travel for journeys under three hours. But increased air congestion, the use of hard-to-reach satellite airports and increased security measures have all played in rail’s favour. “The head of the French railways Guillaume Pepy, said some time ago that this was more like four or five hours now,” says Smith. “Paris to Perpignan on the TGV is five hours and 15 minutes, and SNCF have a 50 per cent share of travellers.”
In fact, high speed lines shorten journey times for those who never even ride on them. “The issue about HS2 is it has been badly publicised by the media,” says Vardy of the UK’s beleaguered £85bn rail project. “Partly to please politicians, everyone shouted about the high speed, but the fundamental of HS2 is increasing capacity.” High speed lines act like a highway bypass: by moving the fastest trains to one line, space is freed up across the existing network to add more slow, regional trains.
Can new technologies push the envelope? Maglev trains - which hover over specialised track on magnetic fields - are freed from catenaries and wheels, and in theory can glide along as fast as air resistance allows. In reality, that currently stands at 603kph, set by Japan Railway in 2015 – not a compelling advance on what has been achieved by a conventional train travelling on line which costs one third as much to build.
In addition, high-speed trains can pick up passengers in centrally located railway stations before switching to high speed lines outside the city. But maglev trains can only run on dedicated track, which isolates them to out-of-town terminals, adding to overall journey time.
Already there are signs the high-speed boom may be over. China Railway Corp has debts of ¥4tn (£446bn), some lines are struggling to attract enough passengers and planned extensions have been shelved. The EU’s high-speed rail network was criticised in an audit for being incoherent, overpriced and under-delivered. Upgrading the line between Stuttgart and Munich shaved 36 minutes off the average journey time, but each one of those minutes came at a cost of €369m (£316m).
“We don’t expect significant network increase in Europe,” says Jarsalé. Instead, his company is focussed on building rolling stock that is more flexible, more comfortable, and more environmentally friendly. Across Europe, state-built networks are being opened to competition. Operators such as France’s low-cost Ouigo will compete with flag carriers on price, comfort and timetabling, and no doubt trade on their green credentials to climate-conscious travellers. Strangely enough, it turns out that with high-speed trains, speed isn’t everything.
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This article was originally published by WIRED UK
