Hi, my idea is the ejector rail.
The ejector rail... just does what it says.
It ejects you off from your minecart when your minecraft is standing on it.
To prevent the ejector rail from ejecting you out of your minecraft, you can power it with redstone or any other redstone outputs/inputs.
I hope you like my idea.
The activator rail already does this, but in reverse - when powered, any mob/player in a minecart going over it will get dismounted.