A common term here for the traffic snarl that results from an accident - or even from a patrolperson writing a ticket on the side - is "gawkers block."
I never see what they're all looking at. Since it's one of the most dangerous situations most drivers encounter with any regularity - I'm too busy to try to get a peek at what they're watching. I'm watching all the gawkers (i.e. EVERY person and vehicle close enough to kill ME,) to see what IDIOT things they're all going to do.