The commotion startled people on the streets, including numerous tourists in the city for the inauguration who are not accustomed to the scares and security presence that have become part of life in Washington.
"We knew security was tight, but this is amazing," said Trey Schroeder, a visitor from Dallas.

The four-hour standoff snarled rush-hour traffic downtown on the first of four days of inaugural events.
(Andrea Bruce Woodall -- The Washington Post)
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Kyle Gaffney, assistant general manager at the Old Ebbitt Grill, said he saw the driver of the van pull up to the security booth and slam on the brakes, making a loud screeching noise. He said authorities rushed out and tried to open the door. But the driver held up something and they backed off.
Gaffney said that officers stood about 15 feet from the van, weapons trained on the vehicle. Another group of police in protective gear stood about 20 feet away, not pointing their guns.
John Taylor, an office worker in the area, said he, too, saw the armed officers approach the van and that he heard much shouting. "It seemed like a movie," he said.
The incident bore similarities to a March 2003 standoff on the Mall, in which a tractor-driving farmer, Dwight Watson, threatened to detonate explosives. Watson, of North Carolina, surrendered after a 47-hour stretch that created snarls during four downtown rush hours.
Yesterday's incident occurred two months after a high-profile protest near the White House. On Nov. 15, a Falls Church man who worked as a federal informant on terrorism was seriously injured when he set himself on fire near the front gate of the White House.
Workers in the area said they were grateful that so many police officers responded so quickly.
"They can go do whatever they need to do to secure our safety," said Jennifer Brooks, who works for a brokerage firm. "It is an inconvenience, but I would gladly sacrifice that."
Staff writers Steven Ginsberg, Sari Horwitz and Clarence Williams and researcher Bobbye Pratt contributed to this report.