Traffic's always irritating. Nothing like being on your way home from work, tired, stressed, etc., and hello, surprise roadwork. And of course no one can take turns at the merge point, they'd rather risk causing a crash by shoving in front without bothering to signal. After all, getting that one car length ahead in 5mph or less traffic is vital to their survival and more than worth trying to harm someone else who's been stuck in that mess ten minutes longer than they have.