Quote from ChicagoBob
So far we have regular rails and detector rails and even powered rails, but what we need now are two more rails that provide a specific function. First we need an Embark rail or pick up rail, this rail is designed that when ever a minecart passes over it if any player is standing next to it they will automatically be placed inside the minecart. And secondly a Disembark rail or drop off rail that does the opposite, when a minecart goes over this rail and if there is a player in the mine cart it will automatically place the player directly behind the mine cart. Perhaps a GUI for the rails so you can select how far away and in which direction a player can be ejected or picked up from. Also a properties file for correcting conflicting Block ID's is always a good idea.
I'd say that the spot you what the peron should be placed should be a pressure plate or something.