High Speed is a relative term; but there are boundaries that we can draw. A high speed train is essentially one that has been built with the key design brief that it must be able to operate at high speed.
There is no defined speed at which you can call a train a high speed train but I have decided to call High speed 125mph (200km/h) and above and I will explain why.
You might say that any thing at or over 100mph (160 km/h) is fast and should be thought of as high speed. Then there is a problem, as you can see by the table, in the UK there are many EMUs which have a top speed of 100mph and not considered high speed, but express trains (ie they miss out unimportant stations). So that would be wrong
Real High Speed Rail purists may argue that you can only call a train a high speed train if it can travel at a top speed of 168mph (270 km/h) and this is the case. In France this is actually the case. Special high speed lines are built for these TGV trains and on "conventional" train lines (ie NOT high speed) the trains are limited to 140mph (225km/h). In fact this is backed up, SNCF have a 140mph engine which is not marketed as a high speed train. Only the TGV is said and marketed to be high speed. The slower sud est TGVs have a top speed of 168mph, as above and the modern TGVs have a top speed of 186 mph (300km/h).
However if you were living in the 1930s in the steam era high speed would have meant 90mph (144km/h) and engines capable of these speeds were generally only used for passenger services and considered express or fast, such as the Class A4. Clearly this is because at the time most steam engines had a top speed of 60mph (100km/h) or 70 mph (112 km/h). It would be ludicrous to say high speed is still 90 mph because so many normal trains are capable of it, as can be seen by the list
Today though it would be ludicrous to say high speed is only at speeds as fast as 168mph or 270km/h. This is because there are so many countries in which 125mph, 200km/h trains are marketed as being high speed such as the Inter-city 125 which has always been called a high speed train. Also in Germany in 1999 a Diesel ICE will be constructed travelling at a top speed of 200km/h again being marketed as high speed. Also among the trains being ordered in the UK there are some 125mph DMU which have been marketed by adtranz as being High-Speed. From this it seems fairly clear that the general feeling is 200km/h high speed.
See Also:
Inter City Trains in the UK - which ones are high speed?
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