FILE - In this July 20, 2017, file photo, a Union Pacific employee climbs on board a locomotive in a rail yard in Council Bluffs, Iowa. This years scheduled completion of a $15 billion automatic railroad braking system will bolster the industrys argument for eliminating one of the two crew members in most locomotives. But labor groups argue that single-person crews would make trains more accident prone. (AP Photo/Nati Harnik, File)

OMAHA, Neb. – How many people does it take to operate a locomotive?

For the railroad industry, the answer is simple: One.

The industry is hoping this year’s scheduled completion of an automatic railroad braking system will bolster its argument to reduce the number of crew members in most trains from two to just one. But labor groups argue that single-person crews would make trains more accident prone.

The $15 billion braking system, known as positive train control, is aimed at reducing human error by automatically stopping trains in certain situations like when it's in danger of colliding, derailing because of excessive speed, entering track under maintenance or traveling the wrong direction because of switching mistakes.

“Technology, in the form of positive train control, does a lot of the work — virtually all of the work — that a conductor does sitting in the cab,” said Union Pacific CEO Lance Fritz.

For that reason, the industry says there is no need for more than one crew member to operate a train — a key issue in contract talks with railroad unions that began in November and could go on for years. Railroads tried unsuccessfully to reduce crew size in previous contract talks.

“I’m 100 percent confident that we would not go down this path if we weren’t certain that fewer people in the cab of the locomotive had no impact on safety,” Fritz said.

Labor groups, however, argue that conductors provide a crucial safety backup in the cab as a second set of eyes to help monitor conditions and the train, and the automatic braking system isn’t perfect.

“Positive train control only keeps trains from wrecking in certain circumstances. There is still a need for a second man in the crew,” said Ron Kaminkow, an Amtrak engineer who serves as general secretary of the labor advocacy group Railroad Workers United.

During a cross-country rail journey, the engineer is at the train's controls, calling out signals and taking directives from dispatchers. All of that is built into positive train control, according to Fritz.

But Kaminkow, who worked for freight railroads earlier in his career, said having a conductor in the cab helps guard against fatigue when engineers and conductors are working irregular shifts with early start times or facing inclement weather.

The National Transportation Safety Board says more than 150 train crashes since 1969 could have been prevented by positive train control, which was required by a 2008 law approved after a commuter train collided head-on with a freight train near Los Angeles, killing 25 and injuring more than 100.

The braking system uses GPS, wireless radio and computers to monitor train position and speed, and it can give engineers commands. Regulators say the system could have prevented the December 2017 derailment of an Amtrak passenger train in Washington state that killed three passengers and injured 57 people.

The automatic braking system is scheduled to be in place on most rail lines by the end of the year. The major freight railroads have the system in place on most of their networks and are now working to ensure all their systems work with the systems on other railroads.

Railroads may decide to keep two crew members on some trains if they know there will be a need to change switches or split out groups of cars at destinations along the route, so it’s not immediately clear how many of the thousands of conductor jobs could be eliminated.

Right now with two crew members, if a train has to stop because a problem has been detected, conductors can walk the length of the train to help identify and address it while the engineer remains in the cab. Conductors can also split a train apart if a crossing needs to be opened for emergency responders.

But if only one person is aboard, that sole crew member cannot leave the locomotive without setting brakes all along the train to ensure it does not roll away.

The solution railroads have proposed for that kind of work is to have conductors stationed in trucks along the route that can respond.

“Conductors play an important role outside of the locomotive, and their work still needs to be accomplished by someone on the ground,” Fritz said.

Still, it’s not clear how long it might take for help to arrive on remote stretches of rail lines in rugged, rural territory. Railroad safety consultant Sheldon Lustig worries about the prospect of long delays when one-person crews have to wait for backup. It could mean rail crossings being blocked for extended periods of time, which hurts emergency response times in affected communities.

“I think there is a trade-off, and it leans in favor of having at least two people in the cab,” Lustig said.

The railroads’ argument to use one-person crews, however, is bolstered by federal regulators’ decision not to address the issue. Last year, the Federal Railroad Administration dropped its proposal to require two-person crews on freight railroads because it said the safety data didn’t support such a rule.

The major railroads and several safety experts believe that operating trains with just one person can be safe. Already, dozens of short-line railroads operate some trains with a single crew member, although their operations can differ greatly from the major freight railroads.

“The data is clear: The safety benefits of having the second person are trivial,” DePaul University Professor Joe Schwieterman said.

Once railroads successfully implement the braking system and can stop trains remotely, the advances might open the door to one day operating trains entirely by remote control or with robots, said David Clarke, director of the University of Tennessee’s Center for Transportation Research. Existing remote-control systems at U.S. railroads are currently limited to use in rail yards.

“I think it’s debatable whether there are safety issues. One person can operate the train, and there are ways to deal with the alertness factors,” Clarke said. “My viewpoint is we could operate the train remotely, and that may be where we are going.”