As a bit of a side note, I saw a video a while back on extreme eco-driving in Seattle I think it was, and this buy was tailgating (about 5-10 feet at times) every truck and vehicle he could to reduce drag. He pulled in front of people then slowed down on hills to ridiculously low speeds, ran stops at twenty MPH and made a total accident waiting to happen of himself. So maybe that guy behind you close enough to read the ID # on your license tabs might be simply trying to save gas.
