It was an accident investigators say didn’t have to happen: Five years ago a commuter train collided head-on with a freight train near Los Angeles, killing 25 and injuring more than 100.

Technology is available to prevent the most catastrophic collisions, but the railroad industry and its allies in Congress are trying to push back a deadline for installing the systems until at least 2020.

The National Transportation Safety Board had urged as far back as 1970 that railroads install technology to prevent the most catastrophic types of collisions, including head-on crashes. The technology is known as positive train control or PTC.

Under a law enacted by Congress a month after the accident, the systems are supposed to be up and running by Dec. 31, 2015. But only a handful of railroads are expected to meet that deadline. The rest of the industry says despite spending billions of dollars on the systems, they face logistical and technical hurdles and need more time. Four senators with industry ties recently introduced a bill to extend the deadline an additional five to seven years.

The delays show how a powerful industry can stall regulations it doesn’t like, even after they’re enacted into law. The NTSB has investigated 27 train crashes that took 63 lives, injured nearly 1,200 and caused millions of dollars in damage over the past decade that officials say could have been prevented had the safety systems been in place.

“This is not an issue where the industry is trying to get out of this mandate,” said Ed Hamberger, president and CEO of the Association of American Railroads. “We have invested too much in it already, and it is in our best interest to get it done as soon as possible.”

But safety, labor and passenger advocates are skeptical that most railroads will ever implement the system without more government pressure.

“When they are pushing for a five-year extension with no changes you have to wonder if they aren’t hoping that some deregulatory White House will come along before then and just lift the burden,” said Ross Capon, president and CEO of the National Association of Railroad Passengers.

Railroads have invested heavily in making their case to Congress. Last year, the industry spent nearly $47 million lobbying the federal government, according to the political money-tracking website OpenSecrets.org. The industry’s 329 registered lobbyists include former Sens. Trent Lott, R-Miss., and John Breaux, D-La., and former Mississippi Gov. Haley Barbour, as well as dozens of former House and Senate aides.

Sen. John Thune, R-S.D., chief sponsor of the bill to extend the safety deadline, has received $672,836 in political contributions from the railroad industry and associated individuals since 1998.

“I think it’s important that we as Congress be careful not to impose undue regulation on the railroad industry,” especially if regulations sap money needed for infrastructure improvements, Thune told a Senate rail safety hearing in June.

Sen. Roy Blunt, R-Mo., one of the bill’s three original co-sponsors, has received $201,969 in rail industry contributions. Blunt’s chief of staff, Glenn Chambers, is the son of prominent railroad industry lobbyist Ray Chambers. Ray Chambers said he doesn’t discuss legislation with his son.

Sen. Claire McCaskill, D-Mo., another co-sponsor, has received $455,995 in rail industry contributions, including $41,768 from Kansas City Southern, which is headquartered in Kansas City, Mo. The third co-sponsor, Sen. Mark Pryor, D-Ark., has received $412,500 in contributions.

The safety system uses GPS, wireless radio and computers to monitor train position and speed and stop them from colliding, derailing because of excessive speed, entering track where maintenance is being done or going the wrong way because of a switching mistake. It’s all aimed at preventing human error, which is responsible for about 40 percent of train accidents.

The requirement applies to Amtrak and 25 commuter railroads, which together carry 564 million passengers annually, and the track they share with freight trains. It also applies to freight-only trains and tracks used to transport a category of hazardous materials poisonous to breathe.