The narrowly averted tragedy on a Paris-bound train, where Americans helped take down an AK-47-wielding gunman, is being seen as a "wake-up call" for the slim security on U.S. railroads. 

The challenge for Amtrak and others has always been that efforts to drastically increase security could slow the systems to a crawl. But while airport-level screening might not be an option, security analysts say the reality is America's rail transit lines are vulnerable. 

“This is a wake-up call, in my opinion,” Bill Rooney, former Amtrak vice president of security, told Fox News.

Amtrak, the largest of 28 U.S. commuter train companies, has more than 30 routes to more than 500 destinations, covering 21,000 route miles daily. That's on top of subway and other rail systems in New York City, Washington, D.C., and elsewhere. Any of these transit lines rely in large part on passengers to be vigilant, and report suspicious activity. 

Rooney, though, argues the “on-and-off strategy about security” isn’t working.

“When you have a security policy, you need follow through,” he said. “It’s not a moneymaker, it’s a business cost. At the end of the day, we do need security.”

He added: "You cannot check everyone, but you can check some and if the bad guy is in and he or she is targeting, they will look at security procedures in place. The more you can show an alertness ... the safer your passengers are traveling that train."

Amtrak is faced with the prospect of some belt-tightening in the near-term, after the Republican-controlled House in June backed a budget cutting funding for the part-government-owned company by $242 million. 

Amtrak gets well over $1 billion from the federal government annually, but the White House and some on the Senate side are fighting the House bill. Funding Amtrak historically has fallen along partisan lines. Many Republicans have pushed for privatization while Democrats have pushed for more government investment and have argued the U.S. is lagging behind countries like Japan and Germany, which pour money into their rail systems. 

Unclear is exactly how much Amtrak is looking to spend on security. Calls to Amtrak by FoxNews.com for comment were not returned. 

The 9/11 Commission Act of 2007 authorized $2 billion for nationwide rail security plus an additional $3.5 billion for transit security through fiscal 2011, according to the Congressional Research Service. 

Amtrak has said it's already making some changes with the resources it has. 

In 2014, Amtrak officials told Congress they would also add more sensors and cameras, and put more patrols on bridges, tunnels and the areas surrounding tracks -- in addition to expanded air and water patrols near the rails.

In 2012, Amtrak’s then-Chief of Police John O’Connor also testified that Amtrak was expanding its security measures, including training employees how to spot suspicious behavior and “layering in” random screening of bags, with canines both on board and in the Amtrak stations.

House Homeland Security Committee Chairman Michael McCaul, R-Texas, told Fox News he supports ramping up current security measures but cautions against changes like patting down passengers.

“Right now, the security at subways and on trains is based on K9s, but also good actionable intelligence,” he said. “In the case of our American heroes that took down this terrorist, it’s just vigilance on the traveling part of the public that did that.”

Amtrak, which has its own police department, lists on its website a range of behind-the-scenes and front-line security measures in place. Passengers are required to show photo IDs when purchasing tickets and before the boarding process begins in some areas like Washington, D.C.’s Union Station. At times, Amtrak carries out a random ticket check. It also relies – heavily -- on passengers to report suspicious activity.

Unlike airlines with single points of staffed access, Amtrak -- and other rail lines like the MTA Long Island Rail Road in New York, Metrolink in California and MARC Train in D.C. -- have multiple points of access and share facilities with other transit systems. Amtrak handles millions of passengers at hundreds of locations daily and has to keep things running smoothly with jam-packed schedules that leave little wiggle room for mistakes.

In response to the 2004 Madrid train bombings that claimed the lives of 191 people and injured 1,800 more, the Transportation Security Administration created Visible Intermodal Prevention and Response squads that work in tandem with officials to monitor train stations.

John Cohen, a former counterterrorism official, told ABC News that trying to execute an airport-style screening process “would essentially make rail travel extraordinarily difficult if not impossible.”