Teams of law-enforcement officials began patrolling transportation hubs yesterday in at least 10 cities, including Baltimore, as a visible deterrent over the holiday, Transportation Security Administration officials said.

Units including canine officers, air marshals and officers trained to observe behavior, called VIPR teams, have been sent to support local transit police at airports and subway stations in cities along Interstate 95 such as Washington, Philadelphia, New York, Providence, R.I., and Boston. Houston, Los Angeles, San Francisco and Chicago also are getting extra attention.


Yesterday evening, pairs of TSA officers were standing inside and outside of Baltimore's Penn Station as commuters and holiday travelers waited for their departures.

"It's good to see them in position," said Lolita Wilson of Forest Park in West Baltimore, who was at Penn Station last night picking up a friend from Washington.


"It's showing Baltimore is in place, in case anything happens."

The Maryland Emergency Management Agency announced plans yesterday to increase staffing at the state emergency operations center for the many events planned for today's holiday.

Representatives from state agencies and departments, including Natural Resources, the State Highway Administration and the Maryland State Police, will staff the Maryland Joint Operations Center to coordinate their efforts.

Although there were no specific or credible threats to the United States, "certainly any time there is terrorist activity abroad, that certainly concerns us," said TSA spokeswoman Ann E. Davis.

Homeland Security Secretary Michael Chertoff indicated over the weekend that the department would be heightening security at airports and transportation facilities.

"TSA's posture was to go on the offensive and deploy our mobile VIPR teams to add that visible deterrent before and after the July 4 holiday," Davis said.

These cities "have large mass transit systems and heavy usage," she said, as well as large Fourth of July celebrations.

VIPR, or visible intermodal protection and response, teams have provided surveillance for events such as holidays and the Super Bowl up to 84 times in the past year and a half, Davis said. The teams are also staffed by aviation and surface transportation security inspectors, Davis said.


These squads, usually unannounced, "are not screening travelers," she said. "We're serving as an extra set of eyes and ears. We're there to support the transit officers in their effort to keep their infrastructure and customers safe."

The size of teams and their assignments vary based on consultations with local police.

There might be a dozen people per shift, with two shifts a day to cover from early in the morning to late at night. The dozen would be broken into smaller groups to cover more sites and move between sites.

"We're just supporting their efforts and providing assistance," Davis said.

Cheryl Stewart, a spokeswoman for BWI Thurgood Marshall Airport, said that the airport was working with federal agencies as well as the Maryland Transportation Authority police.

"There's an increased focus on vigilance and keeping a heightened awareness," she said.


The international terrorist plot in the United Kingdom, the Independence Day holiday and the expected surge of travelers were all reasons for the stepped-up security, Stewart said.

At about 6 p.m., four people in TSA uniforms were standing just inside the entrance to the main waiting room at Penn Station, talking with a person wearing a Department of Homeland Security jacket.

Melissa Riediesel of Charles Village said she noted the staffing as she walked in the train station while on her way to Washington to celebrate July 4. She called it a "helpful reminder."

"Of course, it makes you a little bit worried, because it reaffirms there is a potential threat," Riediesel said. But she doesn't let such fears interfere with her travels, she said.

Stephen Parker, who was reading a paperback book outside Penn Station while waiting for a ride to his Guilford home, said he hadn't noticed additional security at Union Station in Washington.

"I think it's a reasonable response to what's going on in the world," he said.


The Associated Press contributed to this article.