I've been browsing the Erotic Services posting on Boston's Craigslist, and I'm seeing offers for "car dates".  Can someone describe?

Street walker with a computer. Your car is the incall

The whole thing happens in a car parked somewhere hopefully out of sight of other people (or perhaps in sight of others for more of a thrill).

It reminds me of someone picking up a streetwalker for a quickie BJ or FS.