Revelers gathered on the Mall to celebrate the Fourth of July yesterday, combining the traditional hot dogs, parades and pyrotechnics with a sobering nod to post-Sept. 11 reality: a test of evacuation routes to be used in the event of a terrorist attack.

At the end of an otherwise celebratory day, police set "Operation Fast Forward" into motion at 9:50 p.m., just 15 minutes after the fireworks ended. Over the next 45 minutes, officers directed motorists to four evacuation routes, known as E-routes, where green lights were lengthened from 70 seconds to three minutes, followed by one minute of red.

Although the timed lighting appeared to work as planned, at least one area initially experienced slow going. A snag at 12th Street and Constitution Avenue NW resulted from traffic barriers placed by U.S. Park Police to allow pedestrians to leave safely. The barriers created gridlock until they were cleared at 10:10 p.m., with the exercise half over.

Police officers with yellow vests and bullhorns ordered pedestrians to use the sidewalks and crosswalks. And by 10:30 p.m., traffic was moving smoothly.

When the drill ended at 10:35 p.m., lights on a map at the city's command center in the Reeves Municipal Center gradually winked from blue to green. By now, traffic was flowing smoothly throughout the city. "I think it went well," said Michelle Pourciau, deputy director of the D.C. Department of Transportation. "Every quarter except Constitution worked just as we expected it to. . . . As soon as it was opened up, traffic was cleared out."

In an evaluation of the drill that will take days or weeks, the department will examine why there were delays in opening up Constitution Avenue, she said.

After the traffic jams in the District on Sept. 11, 2001, officials expressed concern that the region's transportation web could not handle a citywide evacuation of panicked residents.

At several Metro stations, people were packed shoulder to shoulder. Outside the Archives-Navy Memorial Station, for example, a line of several hundred people stretched a block.

Metro was busy most of the day. By 10 last night, more than 458,000 passengers had gone through the turnstiles, significantly more than the entire day's total of 363,000 on Fourth of July last year. Metro officials attributed the increase to the Nationals-Mets game at Robert F. Kennedy Memorial Stadium and the nice weather.

The evacuation test capped a day traditionally devoted to events that extol the nation's liberties and struck home the significance of a Fourth of July held against the backdrop of war and terrorism. Spectators waited patiently in long lines at security checkpoints and rested on the newly completed granite security walls that encircle the Washington Monument.

The day began with an old-fashioned show of patriotism along Constitution Avenue, with a mile of marching bands, floats and a soaring Uncle Sam balloon that elicited cheers from flag-waving crowds.

Jeff Hicks, 43, of Arlington passed on red, white and blue garb in favor of a more personal show of pride -- a bone, bead and feather breastplate and choker. He said it symbolized protection, healing and peace for POWs and MIAs, veterans and cancer survivors.

"We Indians should be remembered for all we have done in World War I, World War II and other wars," said Hicks, who served in the Navy in the 1980s. "This piece means being proud, of our heritage and for being free."

The Russell family of Clinton, Tenn., clicked pictures of almost every float that wheeled down Constitution Avenue. Faith Russell, 10, wore a red and white beanie covered in metallic blue spikes. She said her visit to Washington was in celebration of her birthday, on July 3, as well the country's.

In the afternoon, thousands of picnickers sprawled near the Washington Monument rose from their blankets and lawn chairs as the U.S. Navy Band performed a round of military marches. Many in the crowd removed their hats and held small American flags aloft.

Not every moment was so solemn. With a high temperature of 89 degrees, vendors reported brisk sales of umbrella hats with red, white and blue stripes and the slogan "USA All the Way." One vendor said he was also selling a lot of playing cards with photos of Saddam Hussein, and firecracker-shaped Popsicles.

Many took a stoic view of the security checkpoints, saying they found them reassuring. At Constitution Avenue and 12th Street NW, 150 to 200 people lined up, making small talk.

"I must have gone 22 feet in one hour," said a frustrated Robbin Jones, 49, of Fort Washington.

Once on the Mall, there was little refuge from the sun's heat. Beleaguered families sought out small, shady patches where they could wait in relative comfort.

Nine medical tents were stationed around the Mall. Personnel reported no major problems.

At the tent by the Vietnam Veterans Memorial, nurses were handing out bottled water, bandages and sunblock. Moira McGuire, a nurse with the U.S. Public Health Service, said the most common problems they had faced were blisters and children smarting from sunblock lotion getting in their eyes.

A hardy few ventured into the sun without fear.

Tina Guentner, 25, and Laura Termure, 26, batted a badminton birdie back and forth. They approached the holiday with the eyes of anthropologists. Termure, a Romanian working as an au pair in Potomac, and Guentner, an exchange student from Germany, found the holiday interesting, if somewhat mystifying. In Europe, they said, fireworks are reserved for New Year's celebrations, while independence days are typically marked by military parades.

"I think the Fourth of July is something that is just so American, you have to see it," Guentner said.

If there was one cloud in the bright blue sky, it was the war in Iraq and Afghanistan. On Independence Day last year, barely 1,000 U.S. service members had died in the two operations, named Iraqi Freedom and Enduring Freedom. This year, the death total has topped 1,900.

The war was on the mind of Dave Baker, 41, a respiratory therapist from Irvine, Calif., who brought his two young sons to Washington on vacation. They visited the Iwo Jima Memorial, a favorite of 11-year-old Alex, who is a World War II buff.

"I want them to think about things and make up their minds," Baker said of his sons. "We have a lot of friends who are in the war, and they hear a lot of different things about it."

For many, a Fourth of July passed in wartime is different than those observed in times of peace.

"To me, it's like we enjoy the freedom of America -- Independence Day -- and knowing that we are having a war and there are armies fighting and we have the privilege of celebrating independence," said Scott Griffin, an occupational therapist from East Berlin, Pa., who was sitting on a blanket at Constitution Avenue and 14th Street NW. "To me that means being here in Washington, being part of that, celebrating the freedom that our boys are fighting for."

Staff writers Jonathan Abel, Fulvio Cativo, Michael Alison Chandler, Nia-Malika Henderson, Nelson Hernandez, Aymar Jean, Caryle Murphy, Philip Rucker, Lindsay Ryan and Sandhya Somashekhar and staff researcher Madonna Lebling contributed to this report.

Michael Evans of Houston watches the fireworks in an embrace with Lauren Gannon of Los Angeles, to whom he had just proposed, at the Jefferson Memorial. She said yes.

Thousands of people watch the fireworks from the Mall. Spectators had to wait in long lines at security checkpoints to get to the Mall yesterday. "I must have gone 22 feet in one hour," one visitor said. Like many of the spectators, Frankie Gonzales, 11, and Catalina Gonzales, 9, of Las Cruces, N.M., held small American flags as the parade passed by.

Members of the Air Force ceremonial guard march down Constitution Avenue during the parade, which also featured floats, marching bands and an Uncle Sam balloon.

Jessica Bates and Randy Lindquist take time out to rest at the Jefferson Memorial. The pair are visiting from San Diego for the holiday weekend.

Members of the National Society of the Daughters of the American Revolution carry a flag during the parade.