In Tokyo Metro, the player meeples each occupy a single grid space on the map. We had owever I can't find anywhere in the rules claiming that meeples can't enter the same location.
After some discussion at our table, we couldn't come up with a strong argument why we should assume they couldn't when it's unstated. The design of meeples nearly the same size as grid spaces could be meaningful, but it also fits with the general minimalism of the game. Blocking could be a strategic element, but it's not necessarily hugely relevant when station builds are much more about turn order and liquidity.
Effectively there are actually 3 separate movement questions here, sorted roughly from weakest to strongest restriction:
- Can meeples end their movement in an occupied space?
- Can meeples pass through an occupied space?
- Can meeples ride trains that already have a player passenger?