Multiple keys problem

Hey all! I’m busy making a GTA1-like flash game, to test some of the new Flash8 effects. I’m having a little problem with checking multiple keys though.
I know what is going wrong, but I’d rather use as little lines of programming as possible. Does anybody have a tip for me, what would be the best way?

Here’s an example of what I mean. I want to send multiple keys to the Walk functions:

// Keys
 onKeyDown = function() {
 	switch (transport) {
 		case ("foot"):