Mary Michael Wagner, "The Last Girl on Earth"

After arguing with her boyfriend, she takes a ride from a stranger.

(from Story Quarterly #41)

Uh, sure hope he doesn't turn out to be a bad guy. Uh-oh, he is. Sure hope he's got a little bit too much humanity to go through with his evil, opportunitist plans. Whew, he does. The surprise ending here was there wasn't much of a surprise ending. But the suspense was fairly intense.
Here's an I Read A Short Story Today Public Service Announcement: Not every stranger who offers you a ride wants to do you harm. I recently accepted a two mile lift to a train station in an unfamiliar town, and totally didn't have to jump from a moving vehicle. That said, I won't likely do it again because I can do without that kind of excitement. It was pretty stupid. I had my hand on the door handle the whole time. Anyway, thanks for the lift, man.

Portishead, "Strangers"