ATLANTA — Atlanta's dreadful rush-hour traffic could be extra nasty for months to come after a raging fire underneath Interstate 85 collapsed an elevated portion of the highway and shut down the heavily traveled route through the heart of the city.Traffic was bumper to bumper on nearby streets as drivers were forced to take a detour Friday, the morning after the blaze caused the concrete to crumble.The collapse took place a few miles north of downtown, and the effects could fall most heavily on commuters from Atlanta's densely populated northern suburbs. They will have to find other routes to work or ride mass transit.Connie Bailey-Blake, of Dacula, 37 miles northeast of Atlanta, waited for a MARTA commuter train to reach her job downtown. She typically drives, often by way of the interstate."I'm supposed to be at work at 9 a.m. and it's 9:15 a.m.," Bailey-Blake said.