The railroad cards in my Monopoly set state different rent amounts "if x R.R.'s (sic) are owned". The obvious interpretation is that the player collecting rent has to own multiple railroads for this to apply. However, in a recent game one of my players suggested that since the cards don't specify who owns the railroad, the rent increase should take into account the total number of railroads owned by any player.
I couldn't find anything clarifying this in the rules that came with my set. I'm guessing tournament play would use the common-sense interpretation of only the rent-collecting player's ownership counting, but is there anything in official rules (or possibly a newer version of the card) that clarifies this further?