Interoperability is a requirement, but there are also regions of the European area where no railways compatible with high-speed trains can be built: mountain regions, isolated regions in general, railways going through tunnels and viaducts.
Interoperabilita je potřebná, ale v Evropě leží i oblasti, v nichž nelze budovat tratě, po nichž by mohly jezdit vysokorychlostní vlaky - horské oblasti, odlehlé oblasti obecně, tratě s tunely a viadukty.