Older cars may not have cellular data, and some new cars (e.g. the Slate electric car) may be specifically designed without cellular connections or with easily removable chips, but so much can still be inferred from omnipresent roadside surveillance.
It's not enough even to have private cars. The solution must be legislation that limits all of: data collected by cars and cameras, data shared among third parties, and placement of cameras without informed, specific, continuing public consent.
And every time flock-style cameras "could have" done some good, the surveillance state's cheerleaders will beat their drums and bleat their demands.
It turns out protesters don't need privacy, either, because of various reasons. Same for women seeking adequate healthcare, I'm sure. Or LGBT people attempting to exist.
Sorry, I am strawmanning a little. Actually, we'll simply have regulations on use. Regulation which will certainly be followed this time by a government with complete disregard for Constitutional rights. Certainly they will never be misused by the police currently stalking their ex-partners with existing surveillance systems despite existing stalking legislation.
I wish the legislation you talked about existed already. I am dismayed by the overwhelming number of people that love being surveilled. Without them, we would have it already.