If you park the car on worldmap, it can only be encountered by players while you are inside the car map too.
So hurry if you fuel up/repair or taking something out of car trunk inside a map.
If you have left the car by exit grid and there is an orange circle on worlmap, noone can just encounter that car there, until you enter the car map again.
If u drive with a car always travel in RT. When u encounter NPCS in RT you will spawn next to car and can exit the map just by clickin the car.
That can be done in a second, and i never got killed so far when i encountered NPCS in RT.
What u NEVER should do is running to exit grid, or even worse is travel with car in TB mode. In TB mode you cannot exit the encounter by clicking
the car but only by walking to the exit grid, which can be deadly like in your case. So remember, travel RT and when u enc something click on car fast.
Many people i know do some kind of "garage" tents too near their favourite city, to park inside this tent and be able to fuel up, repair and stuff in a secure place.