w, again, please don't quote without citing the source by name.
The tone of drive-in is fairly flippant, perhaps more like a tabloid than a serious journalistic description. If the johns stay in their parked cars, it could certainly be compared to a drive-in (= hamburger restaurant where customers eat in cars; cf. Sonic). But that's more a descriptive explanation than an established term, and it's intentionally comical, even bizarre, to people from countries that don't have state-supported prostitution.
As I said in #3, I agree it's not a red-light district (please note the mandatory hyphen) if it's just a parking area.
#4 is also not very good; streetwalkers' should be one word, and patch could mean 'Straßenzug, der traditionell durch Prostitution geprägt ist,' or an area on the street that's considered the territory of one or more particular prostitutes; in either case, not a parking lot, but a section of a public street.