The first test of Washington's downtown emergency evacuation plan is expected to clear the Mall of most Fourth of July revelers tomorrow and speed them on their way within an hour, officials said yesterday.

"A good majority of people will be out of there in that time span," said Douglas Noble, chief traffic engineer for the D.C. Department of Transportation.

The plan, which calls for police to direct the hundreds of thousands of pedestrians and motorists to seven evacuation routes, where green and red traffic signals will run longer, was developed two years ago in response to the Sept. 11, 2001, terrorist attacks. City officials have tried to publicize it, even painting special signs on streets along the routes directing drivers to the Capital Beltway, but they acknowledged that a major test is needed to tell people how they should flee if terrorists were to strike the city.

"We are trying to educate people that in the event of an unfortunate emergency, these are the routes you would use," DOT spokesman Bill Rice said. "The idea is to see in a limited situation how our systems respond, how motorists and pedestrians respond, and work the kinks out on a smaller scale and hopefully never have to use it on a larger scale."

Experts said yesterday that they knew of no other major U.S. city that has recently tested emergency evacuation routes. "It makes perfect sense," said Brian Jenkins, a terrorism expert who co-wrote a report on how transportation, primarily in New York City, functioned on Sept. 11. "There are two ways of learning," Jenkins said. "One is you produce a theoretical plan, put it on the shelf and wait for a real incident. The other is to run a test, see how it works and make corrections. Mistakes are free."

The routes in what is being billed as Operation Fast Forward include Constitution Avenue between 15th and 23rd streets NW; Independence Avenue between Third Street and Washington Avenue SW; and 14th Street between Pennsylvania Avenue NW and C Street SW.

City officials yesterday provided additional details about the test. They said it was designed to start 15 minutes after the fireworks end because planners believe that will give most pedestrians enough time to walk from the Mall to Metro stations while drivers retrieve their cars from garages. Cars will then flood the streets right about the time pedestrian volume is decreasing, which the city hopes will avoid massive tie-ups.

"Typically, you get a big clearance off the Mall right after the fireworks," Noble said. "Waiting 15 minutes allows people to get out of the Mall, get up into town, get to Metro stations, get to parking garages, and then this gets deployed as people actually leave the garages.

"If we did this right at the start," Noble added, "it would be just a mess."

D.C. police officers will direct people from the Mall to the seven evacuation routes, although they will not stop drivers and pedestrians from using other routes if they choose. Along the emergency routes, streetlights will operate on extended cycles of three minutes green followed by one minute red. Planners believe the extra green-light time will speed cars out of town while a minute of red will allow lingering pedestrians to cross streets. At rush hour, D.C. traffic lights typically run 70 seconds green followed by 30 seconds red.

Transportation officials will observe the evacuation from the command center in the Reeves Municipal Center on 14th Street NW, watching televised images from about 50 traffic cameras at the intersections.

City officials chose the evacuation routes, known as E-routes, two years ago as part of the government's massive response to the Sept. 11 attacks. Officials have struggled with how to evacuate Washington during a terrorist attack and have concluded that the region's roads and transit network cannot handle a citywide evacuation. Instead, officials have focused on moving smaller groups from specific locations.

Del. Eleanor Holmes Norton (D-D.C.) yesterday questioned whether the test was poorly timed because it will ensnare tourists, rather than educating the many residents who are out of town for the holiday weekend.

"I'm also not sure exactly what it will prove," she said. "It may be something of a test of mass transportation, but there will be little test of what really stopped us on 9/11, which was lots and lots of cars going the same way."

But law enforcement and Metro officials yesterday said they support the evacuation plan. "This is a twofer," U.S. Capitol Police Chief Terrance W. Gainer said. "We need to move the people off the Mall anyway. Why not use this opportunity to drill your plan and make sure it is working?"

About 125,000 vehicles are expected to travel downtown for the festivities, according to AAA Mid-Atlantic. Metro estimates that more than 300,000 spectators rode trains to last year's Fourth of July celebration, which was marred by rain. More than 500,000 people took Metro to the fireworks display the year before.

The other downtown evacuation routes are Ninth Street between Pennsylvania Avenue NW and Interstate 395; South Capitol Street between Washington Avenue and M Street; Washington Avenue between Independence Avenue SW and South Capitol Street; and Third Street between Constitution Avenue NW and Independence Avenue SW.

Staff writers Del Quentin Wilber and Carol D. Leonnig contributed to this report.

The test of the city's evacuation plan will start 15 minutes after fireworks end because planners believe that will give most pedestrians enough time to walk to Metro stations while drivers retrieve their cars from garages.