OMAHA, Neb. (AP) — When American freight trains delivered cargo after World War II, they commonly had seven people aboard — an engineer, a conductor, up to four brakemen and a fireman.

Since then, trains have grown much longer. And crews have been reduced in size — to five people in the 1970s and two in 1991. Now U.S. railroads want to put a single person in charge of today’s huge locomotives.

For now, freight trains generally have two people aboard — an engineer who drives the train and a conductor who oversees the long line of cars. Railroad executives want to reduce that to a lone engineer, saying advances in safety systems could keep the risks to a minimum.

Labor groups, some federal agencies and people who live near rail lines are skeptical.