The Collaborative International Dictionary of English v.0.48:
bumper-to-bumper \bumper-to-bumper\ adj. moving slowly with little space between; -- used of road traffic. bumper-to-bumper traffic Syn: crawling. [WordNet 1.5]WordNet (r) 3.0 (2006):
bumper-to-bumper adj 1: used of traffic; "bumper-to-bumper traffic"