Happens to me all the time on rt 6. Speed limit is 50 for the most part and I typically drive 55-60 on it. Never fails that I eventually catch someone in a minivan, rav4, crv or Forester doing 40-45. So I give them at least a two second gap and just chill, nothing I can do about it. Then, inevitably, some jackass in a tinted out Accord/Maxima/Camry catches up and rides a few inches from my bumper, like I can do anything about the traffic in front of me. I've been tempted several times to toss a handful of pennies up and out my window... But I digress.

Tl;Dr: route 6 needs some slow vehicle lanes.