In railway and rapid transit parlance, the Spanish solution is a station layout with two railway platforms, one on each side of the track. This platform arrangement allows the separation of passenger streams by using one platform only for boarding and the other one only for alighting. The concept of separate platforms for boarding and alighting has been proven effective at stations with high passenger numbers.
Looking from one train through another, with doors open on both sides, to a third train. At Barking in London, England eastbound Underground trains open their doors on both sides for cross-platform interchange with two main-line services, C2C and London Overground Barking - Gospel Oak, this photograph from inside one of the latter.
Boston's Park Street Under station in 1912. The same platform configuration is still in use.
At least the new main train station stop and the Marienhof stop are being built with a "Spanish solution", ie with a central platform and an exit to the right for the rapid change of passengers (such as today on Stachus) [via Google automated German-English translation service].