My drive is big enough for about 3 cars if they squeeze on. We have a car which normally gets blocked in by the neighbours who use ours without asking.
It also means if we have visitors, they don't have anywhere to park and they have to find somewhere up the street although the roads are skinny and it's a bit of a nightmare (and I guess that's why they won't do it).
They usually get about 5 visitors a day and don't ask if they can use it first.
I wouldn't mind every now and then (which I have said before) but it's almost every day now and I think they're taking the piss.
I've tried speaking to them and they have said that the visitors don't stay for long so it doesn't matter?