Erik S. Lesser/Associated Press

Shoe scans at airport security checkpoints are the leading cause of passenger frustration and delays

The Transportation Security Administration said it had rejected all four devices because they failed to adequately detect explosives and metal weapons during tests at various airports. One of the scanners is now used in airports in 18 countries.

Last September, Secretary Janet Napolitano of theHomeland Security Department raised hopes when she said that research and development on scanning machines was progressing and that air travelers would eventually be able to keep their shoes on.

But nearly a year later, the T.S.A., which is overseen by Homeland Security, said it was not any closer to finding a solution. Lisa Farbstein, a spokeswoman for the agency, would not address why it had rejected the devices.

“But over all, the machines we tested didn’t detect all the materials we were looking for,” she said.

Over the years, the government has tried to streamlineairport security and cut down on long lines and complaints. Elderly passengers and children may go through security screenings without taking off any clothing. And a prescreening program at 20 airports allows approved passengers to keep on their shoes, belt or jackets and does not require laptops and toiletries to be removed from carry-on baggage. The growing use of full-body scanners also allows travelers to go through security lines faster, the government said.

But no part of airport security has drawn more criticism from passengers than removing their shoes, according to the U.S. Travel Association, a trade group in Washington. Passengers say they hate taking off their shoes more than pat-downs and full body scans, the association said.

“It’s had enough of an impact that it has pushed people toward other forms of transportation,” said Robert Bobo, a spokesman for the association.

T.S.A. officials acknowledge the shoe headaches and say the procedure contributes to longer lines at the checkpoints. “The removal of footwear takes time, reduces the efficiency of the checkpoint, creates safety concerns with footwear removal and contributes to passenger dissatisfaction,” the agency said in a blog post last year.

Shoes were ordered off after Richard C. Reid tried unsuccessfully to detonate explosives in his shoes on a flight from Paris to Miami in 2001. Since then, the government says it has found a host of dangerous items in passengers’ footwear and says it will not reconsider the requirement until it is satisfied with a scanning technology.

In 2007, the agency tested a General Electric shoe scanner at Orlando International Airport. The next year, it tested two scanning machines made by L3 Communications at Los Angeles International Airport. But none of them passed agency muster.

It also tested a device called Magshoe, which is intended to detect metal and is made by IDO Security, an Israeli firm, that deploys the scanner in hundreds of airports and cruiseships around the world, including in China, Italy and Israel.

Michael Goldberg, the company’s president, said the machine can detect explosives containing metal, but not plastic explosives.

Mr. Goldberg said the machine performed flawlessly in tests with the T.S.A. But the agency did not think so.

He said no current technology can detect all of the various chemical compounds used as explosives. Current X-ray machines used to scan shoes can detect metal but are not much help in finding liquids or gels that can be used as explosives.

The government has a $1.4 million contract with Morpho Detection, a subsidiary of the French defense giant Safran, to develop a shoe-scanning machine.

Morpho’s scanner can detect chemical compounds and metal objects, said Brad Buswell, the president of Morpho and a former Homeland Security official. “Our device can detect items to see if there is an explosive in a shoe or simply a pair of Dr. Scholl’s inserts,” Mr. Buswell said.

He said the company will be testing a prototype with the T.S.A. this year.

Many security experts say the security agency is too focused on technologies for intercepting things — guns, knives, explosives — instead of focusing on stopping people.

Rafi Ron, the former chief of security for Israel’s Ben Gurion Airport, said the agency should abandon its shoe-removal policy. “They need a more passenger-based approach instead of looking for items,” Mr. Ron said.

The Israeli model is based on interviews and profiles of passengers. Screeners quickly try to decide whether a passenger poses a threat based on reactions to a set of questions.

Critics said the Israeli approach would be unworkable in the United States and cause longer lines. Some 803 million passengers passed through airports last year in the United States. Israel, by contrast, screened about 12 million passengers. Critics also say such techniques can turn into racial profiling and other forms of discrimination.

The T.S.A. said its security measures focus on the risks that passengers pose, and that the vast majority of travelers in the United States would continue to take off their shoes. “It’s going to be a part of air travel for the foreseeable future,” Ms. Farbstein said.