Take one Friday night rush hour at the start of the Labor Day weekend. Add home games for the Orioles, the Ravens and the Redskins. Stir in a Beach Boys concert at the Maryland State Fairgrounds in Timonium. The result? The traffic mix for Sept. 3.

"It's Venus and Jupiter lining up at the same time. It's Halley's comet," said Maryland Department of Transportation spokesman Chuck Brown. "It'll be some of the biggest traffic-generating events all coming together on the same day."

The Sept. 3 Orioles game against the Cleveland Indians is expected to sell out, bringing about 48,000 fans to Camden Yards. Next door at PsiNet Stadium, a preseason exhibition between the Ravens and the New York Giants should lure 30,000 to 40,000.

Down Interstate 95 in Landover, Redskins officials say the 8 p.m. game with Tampa Bay should draw 60,000 or so, the number that showed up for the year's first preseason match.

"I would say it's not a good time to be on I-95," said Lon Anderson, spokesman for the American Automobile Association's mid-Atlantic region. He said Labor Day travel this year is likely to be near record-breaking, because of the healthy national economy. "Friday night rush hours are horrific anyway. People ought to figure it could be gridlocked and give our roads a wide berth on that night."

Sports fans and commuters have had to fight it out on crowded roads before, but Sept. 3 will be the first time the Orioles and Ravens play on the same day in adjacent stadiums. The first--"and the last," said Roger Hayden, director of ballpark operations at Oriole Park.

It wasn't supposed to happen at all, but the National Football League pushed back its schedule by a week this year, prompting the coinciding games. Officials decided on a noon starting time for the Ravens game--seven hours before the Orioles game--to keep disruptions to a minimum, but they know handling the crowds won't be easy.

To help it go smoothly, they're eliminating postgame tailgating at the stadium, to get football fans out before baseball fans show up to use the same 5,000 or so parking spaces.

Chuck Cusick, facilities manager for the Ravens, said traffic patterns will be adjusted to help Ravens traffic exit as Orioles traffic enters the busy downtown area.

"We feel we have all the bases covered," he said. "It's a matter of execution now."

Transportation officials said the subway might be the best bet for getting to one of the Baltimore games. Express buses will run from park-and-ride lots to those games, too, though it will be more complicated for the Ravens game, because the lots will be used by commuters. MTA spokesman Anthony Brown said some parking locations will change to accommodate both commuter and game traffic.

Officials are asking those who can't take mass transit to consider car-pooling. And no matter what, travelers in that area should expect delays, Chuck Brown said.

On the roads, Maryland State Police will have an additional 100 troopers statewide throughout the weekend for beefed-up holiday patrols.

The Maryland State Highway Administration will add more emergency patrols to assist motorists and respond to accidents, and Brown said there shouldn't be any construction to delay motorists around Baltimore.

Electronic message boards from Virginia to Maine will be used to alert drivers to congestion in the Washington-Baltimore region and offer alternate routes. Traffic cameras positioned on I-95 north and south of Baltimore will allow people to visit a Web site (http://www.chart.state.md.us) to look at real-time traffic conditions.

If they can successfully manage the mix that day, transportation officials may do more than score with motorists. As boosters prepare to make a formal bid for the 2012 Summer Olympics, some say this could be the ultimate test: a traffic jam of Olympic proportions.

"It is an opportunity to prove that the transportation system works," said Edward Cline, deputy director of the Maryland Stadium Authority.

Hayden agreed. "The Olympics is not going to provide any more one-day traffic than this," he said.