More than a half-million spectators are expected to line the 14.4-mile route. And volunteers, in kelly green shirts and whistles around their necks, will be on hand to make sure crowds are kept at a safe distance from cyclists.
"People hate us at the end of the day, because all they hear are whistles," said Terri Bateman, 51, a longtime Manayunk resident who has been helping with crowd control at the race since its start in 1985.
Consider what the marshals are up against.
Lincoln Financial Field holds about 69,000 football fans.
Wachovia Center accommodates almost 20,000 spectators for basketball games.
But the cycling course, looping from Logan Circle in Center City to the dreaded Manayunk Wall off Main Street, will be lined with 500,000 spectators - easily more if the weather cooperates, event organizers predict.
To keep fans separate from riders, race organizers rely on more than 300 volunteer marshals. "We hold a little school to teach them how to watch the bike race," explained Jerry Casale, head of logistics for the event sponsor, Threshold Sports LLC of Norristown.
A cycling road race is a different kind of spectator sport. Unlike a marathon race, where runners stretch for miles, cyclists travel in a dense, fast-moving swarm, called a peloton in cycling parlance. Speeds can reach more than 30 miles per hour on straightaways on Kelly Drive, or as fast as 60 miles per hour in downhill stretches like Manayunk Avenue.
"It's one of the only professional sporting events that's free to the public and where you can get real close to athletes," Casale said.
At the Wachovia race, spectators will hear approaching cyclists long before they see them.
Winnie Clowry, co-owner of Le Bus restaurant on Main Street in Manayunk, says that is part of the excitement of the event.