French Train Attack a Reminder of US Railroad Vulnerability

Days after three Americans subdued an AK-47-wielding gunman on a Paris-bound commuter train, Amtrak, one of America's largest passenger rail companies, is reassuring travelers in the states that the carrier is taking security seriously.

"Amtrak has implemented a number of security initiatives to improve safety and security for our employees and passengers," the company said in a statement. "Efforts include the use of explosive detection K-9 teams, passenger and baggage screenings, and strong partnerships with local, state, federal and international agencies - including active participation in FBI Joint Terrorism Task Forces - to share intelligence and conduct joint security exercises."

The security initiatives are ongoing and not in reaction to Friday's attack, the partially government-funded railroad said.

But the reality is that, like airlines, U.S. railroads remain vulnerable to terrorist attacks, experts say.

Despite a significant investment in rail security following the Implementing Recommendations of the 9/11 Commission Act of 2007, some lawmakers have complained that the country remains overly focused on aviation safety - and that train attacks in Madrid, Mumbai and London prove that passenger rail can be a terrorist target.

"The increased security efforts around air travel have led to concerns that terrorists may turn their attention to 'softer' targets, such as transit or passenger rail," a March 2015 report from the Congressional Research Service reads.

"A key challenge Congress faces is balancing the desire for increased rail passenger security with the efficient functioning of transit systems."

If you're a regular rail customer, you've probably noticed that train stations lack the magnetometers and body scanners used at airport terminals to detect guns and knives.

With rail passengers coming and going rapidly throughout the day, establishing airport-style security protocols at train stations "would essentially make rail travel extraordinarily difficult if not impossible," said John Cohen, a former U.S. counterterrorism official and ABC News contributor.

Added ABC News contributor and former FBI agent Brad Garrett: "The idea that you could screen all of those people is not realistic."

Instead, rail security teams are focused on gathering intelligence to protect critical stations, tunnels, and bridges and maintaining highly visible deterrence teams, including a robust uniformed police presence.

Amtrak retains its own police force with over 500 personnel, including canine units that "provide a psychological and physical deterrent to potential threats," plus two analysts with top secret security clearance who routinely sit in on classified briefings with federal officials and coordinate VIP movements, according to the Amtrak Police Department.

And armed Amtrak security personnel perform random luggage searches at bustling hubs like Washington's Union Station or New York's Penn Station.

The TSA - best known for its work in airport security - sometimes joins Amtrak and local police on security sweeps. Established partly in response to the 2004 Madrid train attack, the TSA's VIPR (Visible Intermodal Prevention and Response) squads -- made up of behavior detection officers, security investigators and explosive experts -- work with officials to monitor stations and prevent attacks.

And yet, "notwithstanding all that we do from a rail security prospective," Cohen said, "chances are that if someone wanted to get on a train with a firearm and begin shooting people, there's a pretty good chance that they would be able to do it."

ABC News' Emily Shapiro contributed to this report.