onsdag 27 augusti 2008

Who needs high speed railways?

Finland double deck train interior
Originally uploaded by seadipper

The opening of the new high speed railway between London and the Channel Tunnel last November has led to renewed interest in the idea of constructing one or more high speed railways for travel inside Britain. There is much that needs to be said on this subject. It could turn out to be an expensive prestige scheme of little real benefit.

The first and most obvious point is that it is the door-to-door journey that counts, which is why the private car will remain the first choice for most people’s travel, followed by the bicycle and walking for short trips, especially in towns and cities. People will normally use public transport if they live in a city and have chosen not to own a car, or cannot afford one, or if the roads are too congested, or the journey is long and the train or plane is faster or cheaper. For long distance travel, key factors in the choice will be the ease or otherwise of getting to an airport or main line terminal, and the convenience and flexibility of the booking arrangements; any service that is not available at reasonable cost on a turn-up-and-go basis is going to be relatively unattractive.

The journey to the airport or station is critical. The railways’ claim to provide a city centre to city centre service is not as appealing as rail’s advocates would like to think, because most people’s journeys are not centre-to-centre. The situation at the Eurostar terminal at King’s Cross demonstrates the problem: there is a queue of passengers waiting to catch a taxi, another queue of taxis waiting to get into the taxi rank to pick them up, which they are unable to do because there is yet a third queue, of taxis waiting to get out of the taxi rank onto the congested Euston Road. The time saved by the five billion pound railway is being squandered at the terminal.

Transport planning should take account of the door-to-door journeys that people actually want to make. The five billion pounds that was spent on the Channel Tunnel Rail Link would almost certainly have been more usefully invested on local transport within Greater London. And when high speed lines are constructed, it is essential to complement these with improved local transport. There is no point in rushing people hundreds of miles at high speed from one taxi queue to another.

A related issue is the cost and value of speed. The time taken for a journey is equal to the distance divided by the speed. This leads to diminishing gains with increasing speed: each increase in speed of, say, 10kph, produces a diminishing reduction in the time saved on a particular journey. The implication here is that it high speeds are not worth while for short journeys. The terms are relative, but it is not worth travelling at a maximum speed of more than about 160kph for a 100km journey, whereas for a journey of 300km, a top speed of up to 300kph is worthwhile. For journeys within Britain, there are optimum speeds, and they are lower than the speeds for journeys between cities in big empty countries like France.

One of the aims of high speed railways is said to be to combat the “greenhouse effect”, the argument being that railways use energy more efficiently than aircraft and that in any case, electricity can be generated without giving rise to greenhouse gases – which in practice means by the use of nuclear energy, though it should not be forgotten that greenhouse gases are emitted in the construction of a nuclear power plant and the extraction and processing of the fuel. From the point of view of cutting carbon dioxide emissions, it is a good thing to get people out of cars and aircraft and into trains.

Some basic physics comes in here. Newton’s First Law of Motion says that a body will continue in its state of rest, or uniform motion in a straight line, unless acted upon by a force. A close approximation to this state of affairs would be a stone on an icy surface, which will keep on going unless something gets in its way. An aircraft will not keep going in a straight line because it is being acted on by gravity and if the engines are cut will glide to the ground. So all the time an aircraft is in the air, some work must be done to counteract the force of gravity.

Newton’s Second Law of Motion can be formulated in various ways, and states that if a the force is applied to a particular mass, the acceleration produced is proportional to that force, and, put another way, the force required to produce a particular acceleration is proportional to the mass.

At low speeds, a train on a straight level track behaves in accordance with these laws. In these circumstances, if follows from the Newtonian laws that the energy required to get a train up to a particular speed is proportional to the square of the velocity. Once the train is up to speed, on a level track it should then go on for ever. If the train is going to be stopped, the kinetic energy of the moving train must be converted into some other form of energy through the braking system, or, preferably, back into electrical energy through regeneration or perhaps to mechanical energy through the use of flywheels. It is even possible to brake the train by making it run up a hill, for example, at the approach to a station, thereby converting the mechanical energy into potential energy, ready to be changed back into kinetic energy as the train leaves the station; the Metropolitan Line in London was constructed on this principle in the 1860s and the system has worked effectively ever since, despite a change of traction from steam to electricity.

The two Newtonian Laws apply at low speeds as far as the motion of a train is concerned. The velocity-squared rule is important when it comes to braking and suspension systems, crashworthiness requirements, wear and tear, and so on, which push up capital and running costs. But the energy consumed by high speed trains is mostly in the overcoming of air resistance, due to the viscosity of the air.

Anyone who has ridden a bicycle will know that at speeds of about 10kph, the wind resistance is negligible. At double the speed it is significant and it becomes increasingly so at speeds of up to 40kph, which most cyclists would be unable to keep up for long. This is because air resistance contains a term that is proportional to the square of the speed. For trains, this means that whilst at speeds of up to about 130kph, the air resistance is small, at higher speeds it become increasingly significant. A train running at 300kph will always, however, be using less energy than an aircraft flying at the same speed because it does have to keep itself up in the air, nor does it have to use energy climbing to its cruising height. Nevertheless, the energy savings to be made by switching from air to high speed rail need to be looked at with care. Since there are optimum speeds for different lengths of journeys, it is important to establish what they are and resist the temptation to run faster for the sake of prestige or headline-grabbing figures – though the ability to promote a service through good advertising copy obviously comes into the picture.

In the light of the above, what should Britain’s new high speed railways be like? Obviously they must be engineered for high speeds. But it may be that except on the long runs between London and Glasgow, Edinburgh and Newcastle, the trains will be running at more modest speeds, following the fastest trains in a flighted service pattern. Obviously the route or routes must be able to accommodate trains such as the TGV Duplex. But there are other questions that need to be answered. What about freight, which might run at night? Should the line be constructed to US standards so that it can take double-stack container trains? If the latter is the case, then the passenger trains could be full-sized double-deckers trains like the Finnish example illustrated. And since the line or lines are to be constructed to some other standard than the restricted British one, to what extent should they or can they be used for services running also over the existing routes where the rolling stock is built to the small British loading gauge?

This consideration of loading gauge restrictions implies that the new lines will need their own city centre terminals if the best use is to be made of them. Limitations of space mean that these terminals, and the approach lines to them, will probably have to be underground and very expensive. They will generate huge amounts of land value in their vicinity but in the absence of a land value tax, the value created will disappear into private pockets.

The development of Britain’s railways has been hampered almost from the outset by the decision to adopt too small a loading gauge, with the result that Britain’s trains are no larger than some running on 3ft 6in gauge routes such as those in Japan and South Africa. If new railways are to be built, suitable for the twenty-first century, the planning must look to a hundred years ahead. The overall concept needs to be considered both in breadth and in depth. And some means of paying for it must be found, for example through land value capture, which would prevent the benefits being syphoned off into private hands in the form of enhanced land values.

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