In Boston, it turned out traffic jams are caused by just a few drivers in the grand scheme of things, the Globe noted. "What they found, perhaps surprisingly, is that during rush hour, 98 percent of roads in the Boston area were in fact below traffic capacity, while just 2 percent of roads had more cars on them than they could handle," the Globe wrote. "The backups on these roads ripple outward, causing traffic to snarl across the Hub."