See Giordano's booster pics. I mean at the start of a run, not some way along when it looses speed. I have a tunnel + track from my spawn to my fort, and with a long ramp, and unless I move quick when I bump it, its gone and stopped half way down the 'flat' tunnel. I can remember seeing one where the guy used water and the cart dropped or something and it worked that way... You could rig a loop up with a junction tht leads to your main track so that once your cart gets up to speed and you get in it, you can hit the button from the cart and be coralled onto the main track. Or, have the startting track go the wrong direction for a while, then curve bakc around so that you could push it, then wait a bit for it to come back going the right direction and hop on it as it goes by.