The 1,435 mm gauge also has an historical background. The British engineer George Stephenson used it for the Liverpool and Manchester Railway (the first locomotive-only railway in the world, with no horses pulling carts). With the success of the project, this gauge was applied to several other railway lines.
In most of Europe, trains run on the right, but some countries like the UK, Ireland, Portugal, Belgium, Sweden, Italy, Slovenia and France (except Alsace-Moselle) drive on the left.
Not all high-speed trains use the same voltage. High-speed-trains usually run on 25,000 volts alternating current (AC), but a few countries operate trains above 200km/h with other voltages, such as 15,000 volts AC in Germany, Austria and Switzerland. Some sections of high-speed lines in Italy and Russia use 3,000 volts AC. These other voltages are due to historical reasons.
However, technical specifications for interoperability have been adopted across Europe, which will standardise railway technology, so that in the future trains will be able to cross borders much more easily. At some point, one train will be able to cross the whole of Europe with no big problems.
What is the maximum speed that high-speed trains can reach? How safe are they ?
There is not a standard maximum speed. It depends on the type of train and the type of infrastructure. Like roads, different sections of railway lines have different speed limits. Some trains can reach 300 km/h, some 250 km/h. It depends on the infrastructure. Newer lines in France allow operations at 320 km/h, and in China there are trains that travel at 350 km/h from Beijing to Shanghai.
There are many checks and computer controls on high-speed lines and in high-speed trains. The in-cab signalling takes control of the train, which reduces the risk of human error. The major points of accident on railways are actually level crossings, but on high-speed lines they are not allowed. Existing ones have to be removed, if the speed of an existing line is increased to above 160 km/h.