To have a high speed rail system, making the high speed trains is really the tip of an iceberg. What really makes systems a success or failure is the railway that the run at. Railways like roads have speed restrictions, and like on roads often the speed restrictions are below the top speed of the train. Building a fast train is easy, its building tracks good enough to allow trains to safely and smoothly travel at 160-200mph or 250-320km/h, which are also long enough to allow the trains to accelerate up to these speeds (often many miles) and decelerate is quite difficult.
Since the automobile has become more widespread and with the existence of motorways, where cars may reach speeds of up to 75mph (120km/h) or thereabouts depending on local laws. Standard mainline railway trains running at 100mph (160km/h) have found it difficult to compete with the car, as once journey time to and from the station and waiting for the trains had been calculated, rail travel did no longer offer a significant journey time advantage over the car. In order to attract people to railways ticket prices had to be at the lowest possible, meaning minimal profits. No one would want to build a brand new railway line, the interest payments would crush any company. Not only this but all important inter city routes in Europe are connected by rail, so where else could they go? All this has meant that in the early-mid 20th century new railways were unheard of and some small lines were often closed down because they made a loss.
It seems quite exciting for rail that now today railways are making a come-back. Thousands of miles/km of new railways have been build in the last decade, and new lines are under construction all over Europe. Since 1981 in France over 1000km (600miles) of new track has been laid for high speed trains, with
The primary problem with existing railways is that they can have tight curves. The centrifugal forces on an object going round a bend are the function of the square of velocity, ie if you double the speed, you quadrouple centrifugal forces, if you triple the speed you increase centrifugal forces by nine-fold. Therefore even what might appear mild curves provide problems at speed.
Other key problems are that running on existing railway, the new fast trains have to be sheduled in around the conventional trains. This can be a tricky thing, especially on a busy network, fast trains can easily become stuck behind slow running ones, resulting in delays.
Safety is also a paramount consideration. Although since initial construction 100 years ago the track will have been replaced many times, the foundations of the railways are the same which means after heavy rains for example the track may sag slightly and loose some alignment, only a real problem at speed. Level crossings also form a problem.
Level crossings are the most common reason for accidents on railways, where road vehicles break down or get stuck on the railway and the train crashes through them
All high speed lines are fenced off. Indeed in the UK all railway lines are fenced off anyway, however on continental Europe many railway lines are easy to get onto. High speed lines are fenced off for obvious reasons, to eliminate the risk of any animal or people wandering onto the railway line. Note: Germany is the exception to this, high speed lines in Germany are surprisingly unfenced.
Foundations for high speed lines are much deeper than conventional railways. Usually a layer of concrete and tarmac is put down (like a road) and then the ballast is put on top. This is to try and stop movements in the ground from affecting the alignment of the railway.
The wide spacing between the lines is important because when two trains pass each other the speed difference can be as much as 600km/h or 370mph. If the two trains are too close together this causes at first a burst of air pressure when they first pass and then a drop in pressure during the coaches. Although this isn't enough to push the trains off the track, repeated stress on the windows may cause fatigue and mean they break eventually. So for safety reasons two tracks in each direction are placed further apart than on normal lines.
Gentle curves are key in what high speed lines are about. Tight curves on TGV lines have a radius of about 3 miles or 5 km. This is large but at speeds near 200mph can be felt. Curves are also banked up a lot more than on conventional lines. This is because slow trains will not run on them and it is extremely rare for a TGV to come to a stop because of a signal. This is noticeable when travelling on TGVs by watching the horizon and seeing it change (just like when on an aircraft). Since the degree of banking is calculated to exactly balance centrifugal forces at running speed the TGV you can detect no changes on the forces on you.
Perhaps surprisingly greater gradients are allowed on high speed lines than conventional railways. There are two key reasons for this, first of all modern high speed trains are extremely powerful, TGVs generate as much as 12,000hp, steam engines were no where near as powerful (about 1,000hp) in the era when conventional railways were built. The second reason is that the faster a train travels the less it will slow down for the same rise in height. This is because as it is going fast it takes less time to climb the hill and so gravity has less time to act to slow the train down.
Generally speaking engineers try and avoid tunnels on high speed lines. This is because when a train enters a tunnel at speed it causes large pressure changes. This can be painful and harmful to passengers ear drums. A solution was thought to be to pressure seal trains as with the TGV Reseau, however with very high speed trains (300km/h or 186mph) the pressure changes can be so large it can shatter the windows, particularly when two trains pass in opposite directions in a tunnel with a closing speed of 600km/h or 372mph in a confined space. However German and Italian high speed lines include tunnels but they have subsequent speed restrictions. As a result the best average speeds along German (125mph,200km/h)and Italian (103mph 165km/k) lines are considerably lower than in France (158mph, 254km/h) and Japan (164mph, 262km/h), and even a British conventional railway outperforms the Italian high speed line in terms of speed with an average of 112mph, 180km/h between London and York
It must be emphasized that high speed trains may run on conventional railway but are usually limited to 140 to 125mph (230km/h-200km/h). Most high speed railway services in Europe spend most of their journey on conventional lines, but come together for a fast run on a trunk line.
Japan has a very large number of high speed lines (more than any other country) for the Bullet train. Further information can be found here
France has a large number of high speed lines. The main one is Paris to Lyon, a dedicated high speed line running the whole way has been around since 1981. Branches off allow trains to run off to Dijon, Strasbourg and Switzerland, and the high speed line branches off just before Lyon to by-pass it and then runs onto conventional railway for connections to south of France such as marsielles. More recently iin 1993 a line was constructed going from Paris to Lille and then branched off, one to the channel tunnel, the other high speed line to Brussels. There is a direct connection which by-passes Paris to the Paris-Lyon line, which allows trains to go straight from Lille to Lyon for example without going through paris, however it does stop at Charles de Guales airport. A map of the TGV network with explanations can be found here
The only high speed line in Italy runs between Firenze and Rome, a non-stop service using Pendolini trains taking 1hour 30 mins with an average speed of only 103mph, 165km/h. The line is however visually impressive with a large number of tunnels and viaducts.
The principal high speed line in Germany runs between Wurzburg and Hanover, and part of the railway from Stuttgart to Frankfurt is high speed, and there is a major high speed line under construction which will run between Berlin and Hanover.
The section of high speed line runs from Seville to Madrid where AVE trains run (which are TGVs exported to spain) and Talgo trains run. The advantage of Talgo trains is that they can run on Spanish Broad gauge railway and high speed line (standard guage) as the wheels are designed to change. Therefore Talgo services can use the high speed line for a fast run and then go on for connections on conventional line. The Talgo has a top speed of 220km/h or 138mph. The AVE TGV has a top speed of 300km/h or 138mph
There are two main drawbacks of building high speed railway lines, construction costs and environmental impact. Construction costs aren't really a problem as the income received is usually enough to pay off a high speed railway line, although this has to be weighed against the fact that by not building a new high speed railway line you loose the construction costs and get some of the extra revenue if you run high speed trains on old track. Environmental impact comes in through cutting down trees/re-landscaping for the railways, and creating a brand new transport corridor. However where possible this can be reduced, for example in France the section of high speed line from Lille to Paris was build so that it ran right along side the A1 (a 6 lane motorway), (always very amusing to overtake cars and lorries leaving them very far behind!) This means a new transport corridor isn't created so environmental disruption is at a minimum.
Dedicated high speed rail is only really applicable if it cannot be achieved by conventional railway. Although existing track can be safely run at 140 mph (230km/h) existing track may have a number of speed restrictions because of curves. High speed lines may also be looked at if railways are in saturation and no extra services can be timetabled in. Sometimes when existing railways were built they were constructed a bit at a time and a haphazard network arose. This means train lines often don't go in a roughly straight line between distant locations, often because they go to other towns in between. Building a new line gives the option of building a direct straight line between cities giving a shorter running distance again reducing journey time. However with the advent of tilting mechanisms which allow curves on existing railways to be negotiated with up to 30% more speed, it puts a knife in the case to build dedicated lines.
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