Some time ago I have seen a minecart security mechanism which hid the minecarts below the surface and made them appear on a lever-switch. It appeared between two diagonally placed blocks (viewing from the side). Switching the lever made a door noise inside the system.
In case anyone understands what I am talking about - I am looking for any blueprints or details on this mechanism, do any exist?
Edit: As suggested by James, I used power rails to solve the problem. This system is small, works fine and can even be condensed down to a booster section of 1 block. Note the ladder I put in the IO-tunnel so that the cart doesn't pop out. I will implement vertical wiring as well so it only needs two blocks in width.
Here are some screenshots taken from the system.