Freight railroads would have to employ at least two people on each train under a bill that won preliminary approval in the Colorado Senate on Friday.

The measure, HB1034, is designed to maintain some safety on those freight trains, particularly the longer ones, said one of its sponsors, Sen. Jessie Danielson, D-Wheat Ridge.

"Most trains used to be operated at a minimum of five-person crew, and as the years have gone by that's been dwindled down to two," Danielson said. "Some of these trains are almost three-miles long. When something goes wrong on the tracks, when obstructions occur, there's a wreck, they may be blocking several different crossings at the same time. One person cannot manage that."

While Danielson said the bill is limited to longer, cross-country trains — locomotives with a caboose or engines pulling freight cars outside of a rail yard that are going slower than 30 mph are exempt from the bill — opponents said those exceptions aren't clearly defined enough.

As a result, the bill would place unnecessary controls on smaller rail lines, which make up the bulk of the 14 railroad lines that operate in Colorado, opponents said.

"There's no exemptions for short-line railroads," said Sen. Jerry Sonnenberg, R-Sterling. "There's no exemption for the 12 small businesses in rural Colorado that utilize short-line railroads. If we're not going to be reasonable about this, and address the concerns ... that the sponsor talked about, the trains that are three-miles long, and going to have a one size fits all, then what are we doing?"

Sonnenberg said sometimes, short lines go more than 30 mph, though not for long distances. He also said most trains don't use cabooses anymore.

The Sterling senator tried to amend the bill to ensure that those short-line railroads would be explicitly exempt, but Democrats who control the Senate rejected that attempt.

Danielson said the bill already is clear on its exemptions, which include passenger and tourism trains. She said she's been working with those short-line rail companies and has been assured they are comfortable with the bill as worded.

"This is an effort to make sure that these businesses can continue to conduct business," Danielson said.

The bill, which cleared the Democratic-controlled House earlier this month on a 39-23 party-line vote, requires a final Senate vote. That vote could come as early as Monday. If approved, it will have to return to the House for final action.