The original Fallout was inspired by Wasteland. Wasteland was inspired by the https://www.youtube.com/watch?v=akX3Is3qBpw movie trilogy. Mad Max movies are about https://www.youtube.com/watch?v=akX3Is3qBpw in the post-apocalyptic world. Fallout 4 should introduce vehicular combat to the series:

New character skills and talents that are related to vehicles: driving and handling of cars, trucks, motorcycles; vehicle marksmanship, ability to salvage parts from other vehicles, vehicle repair, mechanics and maintenance, etc.

Upgradable and customizable vehicles.

Missions based around vehicles: delivery, escort, etc.

In short, Bethesda should apply Rage to Fallout.

the character you create are already better than most npc and monsters you meet , last thing we want is something complete unbalanced as driving around in a tank and making the pc invulnerable

I don't believe so; it depends on the vehicle. Supermutants or http://i271.photobucket.com/albums/jj125/Gizmojunk/bad_idea.jpg~like tearing tinfoil wrapped around corn on the cob.

NPCs could lay ambush and cripple the car; or hit it with a rocket (or a fatman since they littered the gameworld with those diminutive nukes).

And if neither of those, then they could assault car to car.

If FO4 had a vehicle, it could play rather a bit like Brutal Legend where we see the car; only some of the NPCs might have comparably armed cars.

**Alternatively: The car could [again] be rather unique, and it's use for the most part restricted to outside a settlement, and as such, it empowers the PC in the open wastes; effectively being big power armor that increases their speed of travel... which could hopefully demand a return [to the series] for reasons to need to travel quickly.