I need a movie title...?

So I've been trying to think of this movie's title for forever now. I
only remember bits and pieces. Hope this helps.
-It starts out with a couple driving on a highway in what I believe is
called a "convoy ?"
( Where 3 people drive the same speed on the highway, basically, in a
row. )
-I believe they start following a trucker and he turns out to be a
serial killer.
This is really all I can remember. Sorry if I'm not much help.