The Transportation Security Administration has spent a lot of money on technology to keep dangerous items off planes — with mixed results — but has been slower to address another risk: travelers who are using a fake boarding pass or identification.


Despite announcing plans last fall to test machines that can electronically verify passengers’ documents, the agency still relies on its agents to visually inspect boarding passes and IDs, and confirm that each traveler matches the photo on a driver’s license or passport. At a busy airport, one employee may check several hundred documents an hour.


The repetitiveness of that task has left plenty of room for human error, as Michael Krug and his colleague discovered when they were on a Delta flight in February and realized they each had a boarding pass for seat 12C, both printed with Mr. Krug’s name.


“The person at security didn’t notice that my co-worker’s boarding pass had my name on it and he had an ID with his name,” Mr. Krug said.


The two men checked in as part of a group and figured that the agent must have handed them two copies of the same boarding pass, a mistake that was overlooked at the security line and then again at the gate. That triple error may be rare, but it highlights a security flaw that has been publicized many times.


Last year, for instance, a Nigerian man managed to fly free from New York to Los Angeles with an expired boarding pass in someone else’s name, but was arrested a few days later at Los Angeles International Airport when he tried to fly to Atlanta using another expired pass.


Travelers, security specialists and the news media have reported many other instances when T.S.A. agents failed to notice a fake or expired boarding pass or improper identification, a vulnerability that has been a concern since it was discovered that many of the 9/11 hijackers had obtained fraudulent IDs.


With the advent of online check-in, it became easy to digitally alter a real boarding pass with a different name or new travel date and print a copy that would get through security. There have even been Web sites that generated a fake boarding pass or provided instructions on how to make one at home.


The T.S.A. said it was working to address this problem as part of its shift toward a more risk-based approach to screening passengers, which gives higher scrutiny to travelers the government knows less about.


In October, the agency announced that it was spending $3.2 million to buy 30 document authentication systems from three vendors, which it planned to test in airports in early 2012. Those tests are now expected at select airports “in the coming months,” said Greg Soule, an agency spokesman.


“The technology is designed to read security features embedded in both the boarding pass and ID to verify their authenticity and ensure the names match,” Mr. Soule said in an e-mail.


He declined to address why it had taken so long to introduce what the agency was calling Credential Authentication Technology — Boarding Pass Scanning Systems.


But digital readers that can scan boarding passes, driver’s licenses and passports have been around for years, and those documents follow standards that make them easier to read.


The airline industry, for instance, has shifted to using two-dimensional bar codes for printed and electronic boarding passes, phasing out the magnetic stripes and one-dimensional bar codes that once appeared on boarding passes.


In the United States, driver’s licenses and state-issued identification cards also have two-dimensional bar codes on the back of the card, said Geoff Slagle, director of identification standards for the American Association of Motor Vehicle Administrators.


When scanned with an electronic reader, that bar code reveals information that is on the front of the ID or driver’s license, including the person’s name, birth date, gender and address, license number, expiration date and issuing state.


“Any smartphone is capable of reading and decoding these 2-D bar codes,” Mr. Slagle said, although the device would need special software.