Looks like it's all an optical illusion, which is very interesting:
"In the real world, we can’t manipulate the retinal images of cars," said [University of Toronto mechanical engineer Paul] Milgram. "But we thought we could change the image of taillights. We guessed that if we could make a taillight system that appeared to change in size, it might have a significant effect on braking behaviour."In unrelated news, images of Alison Krauss have proven to change the size of more than just the retinas of the C!C!C! staff.