WASHINGTON — As hundreds of commuters emerged from Amtrak and commuter trains at Union Station on a recent morning, an armed squad of men and women dressed in bulletproof vests made their way through the crowds.
The squad was not with the Washington police department or Amtrak’s police force, but was one of the Transportation Security Administration’s Visible Intermodal Prevention and Response squads — VIPR teams for short — assigned to perform random security sweeps to prevent terrorist attacks at transportation hubs across the United States.
“The T.S.A., huh,” said Donald Neubauer of Greenville, Ohio, as he walked past the squad. “I thought they were just at the airports.”
With little fanfare, the agency best known for airport screenings has vastly expanded its reach to sporting events, music festivals, rodeos, highway weigh stations and train terminals. Not everyone is happy.
T.S.A. and local law enforcement officials say the teams are a critical component of the nation’s counterterrorism efforts, but some members of Congress, auditors at the Department of Homeland Security and civil liberties groups are sounding alarms. The teams are also raising hackles among passengers who call them unnecessary and intrusive.
“Our mandate is to provide security and counterterrorism operations for all high-risk transportation targets, not just airports and aviation,” said John S. Pistole, the administrator of the agency. “The VIPR teams are a big part of that.”
Some in Congress, however, say the T.S.A. has not demonstrated that the teams are effective. Auditors at the Department of Homeland Security are asking questions about whether the teams are properly trained and deployed based on actual security threats.
Civil liberties groups say that the VIPR teams have little to do with the agency’s original mission to provide security screenings at airports and that in some cases their actions amount to warrantless searches in violation of constitutional protections.
“The problem with T.S.A. stopping and searching people in public places outside the airport is that there are no real legal standards, or probable cause,” said Khaliah Barnes, administrative law counsel at the Electronic Privacy Information Center in Washington. “It’s something that is easily abused because the reason that they are conducting the stops is shrouded in secrecy.”
T.S.A. officials respond that the random searches are “special needs” or “administrative searches” that are exempt from probable cause because they further the government’s need to prevent terrorist attacks.
Created in the aftermath of the Sept. 11, 2001, attacks, the T.S.A. has grown to an agency of 56,000 people at 450 American airports. The VIPR teams were started in 2005, in part as a reaction to the Madrid train bombing in 2004 that killed 191 people.
The program now has a $100 million annual budget and is growing rapidly, increasing to several hundred people and 37 teams last year, up from 10 teams in 2008. T.S.A. records show that the teams ran more than 8,800 unannounced checkpoints and search operations with local law enforcement outside of airports last year, including those at the Indianapolis 500 and the Democratic and Republican national political conventions.
The teams, which are typically composed of federal air marshals, explosives experts and baggage inspectors, move through crowds with bomb-sniffing dogs, randomly stop passengers and ask security questions. There is usually a specially trained undercover plainclothes member who monitors crowds for suspicious behavior, said Kimberly F. Thompson, a T.S.A. spokeswoman. Some team members are former members of the military and police forces.
T.S.A. officials would not say if the VIPR teams had ever foiled a terrorist plot or thwarted any major threat to public safety, saying the information is classified. But they argue that the random searches and presence of armed officers serve as a deterrent that bolsters the public confidence.
Security experts give the agency high marks for creating the VIPR teams. “They introduce an unexpected element into situations where a terrorist might be planning an attack,” said Rafi Ron, the former chief of security for Ben-Gurion International Airport in Israel, who is now a transportation security consultant.
Local law enforcement officials also welcome the teams.
“We’ve found a lot of value in having these high-value security details,” said John Siqveland, a spokesman for Metro Transit, which operates buses and trains Minneapolis-St. Paul. He said that local transit police have worked with VIPR teams on security patrols on the Metro rail line, which serves the Minnesota Vikings stadium, the Mall of America and the airport.
Kimberly Woods, a spokeswoman for Amtrak, said the railroad has had good experiences with VIPR team members who work with the Amtrak police on random bag inspections during high-travel times. “They supplement our security measures,” she said.
But elsewhere, experiences with the teams have not been as positive.
In 2011, the VIPR teams were criticized for screening and patting down people after they got off an Amtrak train in Savannah, Ga. As a result, the Amtrak police chief briefly banned the teams from the railroad’s property, saying the searches were illegal.
In April 2012, during a joint operation with the Houston police and the local transit police, people boarding and leaving city buses complained that T.S.A. officers were stopping them and searching their bags. (Local law enforcement denied that the bags were searched.)
The operation resulted in several arrests by the local transit police, mostly for passengers with warrants for prostitution and minor drug possession. Afterward, dozens of angry residents packed a public meeting with Houston transit officials to object to what they saw as an unnecessary intrusion by the T.S.A.
“It was an incredible waste of taxpayers’ money,” said Robert Fickman, a local defense lawyer who attended the meeting. “Did we need to have T.S.A. in here for a couple of minor busts?”
Representative Bennie Thompson, Democrat of Mississippi and ranking member on the House Homeland Security Committee, which has oversight of the T.S.A., said he generally supports the VIPR teams but remains concerned about the warrantless searches and the use of behavior detection officers to profile individuals in crowds.
“This is a gray area,” he said. “I haven’t seen any good science that says that is what a terrorist looks like. Profiling can easily be abused.”
Mr. Thompson said he also had questions about the effectiveness of the program because of issues like those raised in Houston and Savannah.
“It’s hard to quantify the usefulness of these teams based on what we have seen so far,” he said.
An August 2012 report by the inspector general of the Department of Homeland Security raised similar questions.
Some T.S.A. officials told auditors that they had concerns that deploying VIPR teams to train stations or other events was not always based on credible intelligence.
The auditors also said that VIPR teams might not have “the skills and information to perform successfully in the mass transit environment.”
Mr. Pistole said the agency is now retraining VIPR teams based on recommendations in the report and is working to increase the public’s knowledge about them.