swapDepth in a playing movieclip (no buttons/clicking)

Hi,

Ok, I have 2 mcs in the same layer: mc_bus and mc_cardrive.

What happens is I've used the the bus and car mcs to drive on both sides of the road in the animation (they will go across the screen then flip over and drive back within their respective mc).

When they first cross over they are layered right but because of the timing of each animation, there is a point where both are going the same way on the same side of the road. At this point the bus pulls up higher (to the side of the road to pick people up) and the car passes it. The problem is when the car passes it is registered as being behind the bus (which would be hitting people).

So i'm trying to get the car to swapDepths and come to the front Only when driving on one side of the road, so only at a certain frame reference essentially - not the entire mc.

Is there a way to use swapDepths in the midst of the animation? without having a button or key event to register it as every other tutorial ever about swapDepth uses?

Thanks