How do trains cross borders?

Before 1945, to prevent the transport of troops, countries organised their rail systems in an entirely independent fashion.
As a result, every country’s rail system is different. Even today, to cross a border, a train has to adapt to:

How do trains cross borders?

To successfully cross borders, a train must be able to adapt to the characteristics of the railways of the country in which it arrives. At the border, several adaptations can be made to the train, with regard to:
– the track gauge, by changing the axles and bogies, or by widening/narrowing the distance between the wheels,
– the power supply voltage (with multi-voltage trains),
– platform height: this is particularly necessary for people with reduced mobility.
– since the external dimensions of the trains themselves can not be altered, the trains are chosen according to the constraints of each country.

More information - Train operation