I've had this happen in many mods, Winterberg, Florian Hamburg, LA too I think. They move either because of danger (person with gun, fire etc.) or because a vehicle with a siren makes them move. In most cases they start walking again. In others they just stand still, and you have to send the police in to move them. In Winterberg this isn't such a major problem. If you're getting too heavy traffic jams, even after removing the person in the road, you can call in the police helicopter. It has a button to reset traffic, IE remove all civilian traffic from the map and respawn it.