Amtrak (search) and commuter rail passengers at one suburban station will have to walk through an explosives detection machine and have their bags screened in a new security experiment designed to frustrate terrorists.

The Transportation Security Administration (search) was beginning a pilot project Tuesday at a rail stop in a Maryland suburb of Washington. Passengers were to walk through a "puffer" machine, which sucks in the air around them and within seconds determines whether they've been in contact with explosives.

Jack Riley, director of the public safety research program for Rand Corp. (search), a think tank, said harried commuters probably won't like being screened.

"Anything that lengthens their rail experience is just going to meet with resistance," he said.

TSA spokeswoman Yolanda Clark said the agency hopes passengers will see it "as another ring of security in another mode of transportation."

The 30-day pilot program also includes a baggage screening machine (search) used in overseas airports. The TSA wants to see how well the machines work in a passenger rail and commuter environment.

Amtrak and a commuter railroad service use the station in New Carrollton, Md., about 9 miles northeast of Washington.

The TSA announced the project in March, soon after terrorist bombings on trains in Madrid killed 191 people and injured more than 2,000. The FBI and the Homeland Security Department (search) have warned that terrorists might strike trains and buses in major U.S. cities using bombs concealed in bags or luggage.

Since more than half of Amtrak's 500 stations are unstaffed, screening all passengers is nearly impossible.

TSA spokesman Mark Hatfield said of the experiment, "We're looking to get a lot of data that's going to help us look at ways it can be deployed and eliminate ways that it won't be practical."

A key problem in screening railway passengers is doing it quickly enough that trains still run on time. That is not supposed to be a problem with the puffer machine, made by General Electric.

The machine - formally called EntryScan (search) - already is used in power plants and military installations in the United States and Europe.

GE spokesman James Bergen said every person constantly radiates as much heat as a 100-watt light bulb in a "human convection plume." The puffer machine has a hood that catches the optimal amount of plume, he said.

If someone has a bomb or has been in contact with one, the plume will carry traces of explosives into a detector that measures the wavelength of the energy coming off the particles.

Some passengers also will be asked to put their bags through a machine that uses X-ray technology to determine what's in them. The machine, made by L-3 Communications (search) of New York City, is used in overseas airports, as well as at the Statue of Liberty (search) and in government buildings on Capitol Hill.

The Rand Corp.'s Riley said he doubts the equipment will be practical on a day-to-day basis. Screening rail passengers might make sense for certain events, he said, such as the upcoming political conventions.

Only passengers on Amtrak and the Maryland Transit Administration's (search) MARC commuter rail system will be affected. A Washington Metro train also stops at the New Carrollton station, but those passengers won't be part of the study.