WASHINGTON -- Security for subways and commuter trains varies by city, but one thing all mass transit systems share is this: They're vulnerable to attack and no technology on the horizon promises to change that.
The Homeland Security Department has looked at high-tech ways to improve transit security but hasn't instituted anything since testing a system last year. Security officers and bomb-sniffing dogs remain the primary ways to combat terrorists.
Rafi Ron, former head of security at Israel's Ben Gurion Airport and now a security consultant in Washington, said there are no technological quick fixes for mass transit systems.
"Very little technology can be applied in this area in an effective way," Ron said.
The reason is fairly simple: Mass transit systems exist to move large numbers of people quickly over a large metropolitan area. Anything that slows down the process, such as security checks, would severely disrupt the systems.
Following the March 11, 2004, train bombing in Madrid that killed 191 people, the Transportation Security Administration tested a high-tech security system at a suburban Maryland commuter train stop. Walkthrough portals "sniffed" the air around passengers to check for explosives residue.
The agency said the tests went well but none of the machines have been installed at train stops. They are being used at some airports.
Homeland Security Department spokesman Russ Knocke said the pilot project showed such technology could be used if a specific threat were directed at a specific transit system.
The TSA also experimented with screening checked baggage on long-distance Amtrak trains leaving Washington's Union Station. Screeners used a combination of X-ray machines, bomb-sniffing dogs and handheld wands that sense minute traces of explosives.
Amtrak spokeswoman Marcy Golgoski said there aren't any TSA programs to screen people or bags at the passenger railroad stations.
"They were happy how the testing went, but I don't know if they decided anything on the testing," Golgoski said.
In another test, the TSA screened passengers as they boarded trains.
"Screening for explosives at airports and airlines makes abundant sense," said Jack Riley, a homeland security expert at the Rand Corp. think tank. "Screening for explosives on trains is going to be expensive and time-consuming."
And so transit officials, after learning of the terrorist attack in London, resorted to traditional low-tech ways to provide security.
In New York City, which has by far the largest transit system, police patrols were increased, more packages were inspected and bridges and tunnels were put under more intense surveillance. In Washington's busiest subway stations, officers roamed the crowds, stood near ticket entrances or led bomb-sniffing dogs through the trains, changing cars at each station.