Vehicles won't activate events that would normally be activated by the hero. The way around this is to use a parallel process that checks your position and teleports if you're within a certain area.
In other words, <>Memorize Location, and use nested branching to check to see if you're on the right square(s).
In the below example, I want to make it so that when I'm hovering over the two highlighted squares, I warp to another map (some sort of volcano-related area). So I want to be where the X>3, X<6, and Y=3. (If you don't know your coordinates, you can find them at the bottom of the screen, in the RM2k3's status bar.)
Code:
<>Memorize Location
<>Branch if Y=3
<>Branch if X>3
<>Branch if X<6
<>Teleport to volcano map
<>
: End
<>
: End
<>
: End
Just have this on the map running as a Parallel Process and it should be fine.