First: I would like to apologize for mistakes in text, because English is not my native language. Second: this is very simple idea so I am sorry if someone suggested this before.
Every time I play Cataclysm DDA I play it for fun and vehicles are part of fun for me. I think I am not only one who wanted to lock some zombies in truck and deliver them somewhere. I never coded anything so I do not know how hard it is, but I made a list of features needed to achieve this.
Zombies have to be able to drive in vehicles. I noticed, that when I hit zombie with a car, it has a chance to appear inside my vehicle (I never checked if my roof is all right so maybe they fell trough roof inside(if not it would be another nice feature)) but when I continue driving, the rest of a car runs through them.
Doors which can be controled with vehicle controls + something to lure zombies on. I know someone just suggested it, but i just wanted my list to be complete.
Last and most problematic feature: ability to walk through vehicle when it is positioned obliquely (I am not sure if this word is right). I think that in game like this there is only one way how to solve it. It would check every vehicle in its base position (position vehicles have been spawned or constructed) and check accessibility of each tile and that tile would be accessible from other tiles in any position of vehicle.
. . .|HH. . . . . .789. . . . . . . .|HH. . . . . . . .789. . .
. . .|^H. . . . . .456. . . . . . .|^H. . . . . . . .456. . . .
. . .|HH. . . . . .123. . . . . .|HH. . . . . . . .123. . . . .
On the left there is part of our vehicle. We are at tile ^. If we press numbers 1, 4 and 7 nothing will happen and if we press 2 3 6 9 8 we will move to tile with that number. (this is very simple, i just wanted to make sure everyone understands my drawing)
On the right our vehicle moved but accessibility of each tile remain same. If you press 9 you will move two tiles away, but in terms of our vehicle it is just one tile. Now if you press 7 you would ran into board not out of vehicle.
If you run out by pressing 6 twice, your movement will return to normal until you try to enter the vehicle again. Whe you try to enter the vehicle it will again compare your movement with accessible tiles of vehicle.
I think this is the last part vehicles need to be nearly perfect, and I also think the work with coding is really worth it.
Sorry for any mistakes in this system if there are any.