In the demonstration games we ran at Salute and Partizan we had a lot of civilian vehicles on the roads. At the end of each movement turn we then rolled randomly for the distance each one moved.
Any figure that was in front of the vehicle and in its movement path simply made a pluck roll.
If they succeeded they moved out of the way, if they failed they were mown down and out of the game.
In one incident a Milk Cart ran through a combat between four Tong Members and three Incorrigibles. All four Tong Member nimbly somersaulted out of the way of the panic-stricken horse and its driverless cart (note: artistic licence being employed for narrative effect). The three Incorrigibles were not so lucky and all went under the hooves and wheels.
As you can imagine much hilarity ensued...

What I'm getting at is apply the KISS principle. If the vehicle is moving give figures a chance to get out of the way. If it is not moving then the vehicle is a sitting duck. It is why in the wars that followed tanks deployed in street-fighting would not advance without close infantry support.