We have free range peafowl and they never get on the cars, but the house and telephone poles and trampoline (LOL!) YES! They will roost where ever they can. I was told by an old timer you can train them not to get on the cars by blowing an air-horn at them any time they come near the cars. I would guess a water hose would do the same trick. They don't like confrontation so will prolly stay away with out too much work.
My father in law used to live in a small neighborhood in the middle of no where. There was lots of peafowl that just roamed the whole place. No one owned them any more.. They roosted on the cars. They also ate the paint off of the cars.. Finally every one that lived around there ended up having a peafowl BBQ....
A friend of mine had this problem with her peas. Not only did they roost on neighbor's cars, they fought their reflections and killed the paint. My friend had to pay the repairs and re-home her peas. So sad.
I think my peas are drawn toward the cars. They seem to know which cars are the nicest and choose them. They absolutely love the golf cart when its parked under the awning. There is just enough room for them to perch and not hit there head -- especially when its raining.