A pilot program in Washington, D.C., to screen rail lines for explosives is one step administration officials say they have taken to boost rail security, but structural difficulties make train travel harder to protect than airways.

Because of the few options for rail routes and the fact that most routes travel directly through population centers, it is impossible to divert hazardous materials from tracks such as those within sight of the U.S. capitol, said Transportation Security Administration (search) Deputy Director Steven McHale.

It is "much more difficult in the rail environment because it is a much more open system" than air travel, McHale told lawmakers last Wednesday during a hearing that emphasized the gap between efforts to protect U.S. trains and air flight.

Since Sept. 11, 2001, the United States has spent $11 billion to make air travel safer, but Congress has allocated just $150 million to improving rail safety, said Washington, D.C., Del. Eleanor Holmes Norton. A number of bills to boost rail security funding have passed congressional committees, but have not been passed by the full Congress.

McHale acknowledged that the Department of Homeland Security (search) spends far more money on air security than rail security, but an accurate assessment of money spent would take into account funds spent by rail companies, local and state governments. He did not say how much the spending totals.

Lawmakers began taking a renewed interest in rail security after the March 11 Madrid bombings alerted them to the exposure U.S. rail lines face.

"We all know in the light of the Madrid bombing that rail is a big vulnerability," Rep. Jim Turner, D-Texas, ranking member on the House Homeland Security Committee, said during a subcommittee hearing last Wednesday. Turner said he wanted to know why TSA officials haven't come to Congress seeking more funds.

"Why is it that TSA didn't request any specific grants?" he asked administration officials.

Rep. Ed Markey, D-Mass., railed against the TSA about steps being taken to divert hazardous materials from population centers and to provide better security on tracks.

"Although we have seen what happened in Madrid, we have deployed just a fraction of the resources possible," Markey said while holding a blown-up photograph of a train hauling a load of dangerous hydrochloric acid within sight of the U.S. Capitol.

McHale responded that despite the challenges of securing rail lines, a lot is being done. To guard against attacks on hazardous cargo shipments, TSA is inspecting the track beforehand and providing additional security, among other measures. On passenger trains, TSA is providing more bomb-sniffing dogs and passenger screening, he added.

McHale said rail security is harder to ensure because unlike air passengers, who board and exit the aircraft at the same locations, rail transit passengers can travel without reservations and have several spots on the platform to enter and exit the train. Additionally, many more rail passengers travel each day than do fliers.

Those challenges make passenger screening a much different challenge, McHale said.

TSA launched a pilot program earlier this month to screen people and bags getting on Amtrak and Maryland Rail Commuter service trains at the suburban Maryland New Carrollton station. The station also services Metro's Orange Line, which travels into Virginia, but those passengers will not be affected by the project.

The Transit and Rail Inspection Pilot (search) will last 30 days and is intended to evaluate the use of emerging technologies to screen transit and rail passengers and their carry-on items for explosives.

"The TRIP pilot project is one of many steps DHS is taking to enhance rail security. As we test these new processes and technologies we expect to learn valuable lessons today that will allow us to better protect rail passengers tomorrow," Asa Hutchinson, DHS under secretary for border and transportation security, said in announcing the project.

Passengers place bags and other carry-on items on a conveyer belt for screening. They walk through a portal in which they feel several quick puffs of air. This process screens for explosives, and passengers are allowed to keep cell phones, keys and other metal objects.

Because the pilot program focuses on explosives, passengers will also be able to carry many items through the screening checkpoint that are prohibited on aircraft, such as scissors and pocketknives.

When the program is concluded, TSA will conduct tests of the ability to screen luggage at Washington, D.C.'s Union Station, as well as check for threats on the trains themselves.

In March, Homeland Security Secretary Tom Ridge announced three areas for enhancing rail security: technological innovations, including biological and chemical countermeasures; threat response capability; and public awareness.

TSA has offered some security awareness tips for passengers, including to be on the lookout for suspicious activity, be aware of items or devices that are hidden or abandoned and contact local law enforcement if they observe a threat.

Speaking not only of rail security, but also of America's transportation system more broadly, McHale said: "Much has been accomplished. Much remains to be done. We look forward to the challenge."