It took just minutes Tuesday afternoon to open four construction bids for the Southwest light-rail line, the most expensive public works project in state history.

The bids submitted by four construction partnerships ranged from $797 million to $1.08 billion, but it’s unclear which group will prevail. The Metropolitan Council, which will build and operate the $1.9 billion line, will decide this fall after staff scrutinizes each bid packet.

Met Council officials won’t say whether the bid amounts submitted fit within budget projections for the 14.5-mile line between Minneapolis and Eden Prairie.

But after the bid opening was delayed three times over the past six months, they were relieved Tuesday following the brief meeting.

“This is a big milestone,” said Mark Fuhrmann, Metro Transit’s deputy general manager.

The Southwest project is enormous, involving 15 passenger stations, 29 bridges, modifications to seven existing bridges, construction of two train and six pedestrian tunnels, 117 retaining walls, and laying miles of track.

“We received hundreds of technical questions from prospective bidders,” said Fuhrmann, a light-rail veteran working on his eighth such project. “Each project is very different, but this is the most complex from a structural point of view.”

If all goes according to plan, construction will begin next spring, with service on the line starting in 2021.

One challenge facing big construction projects like Southwest is a workforce shortage in Minnesota, said Tim Worke, chief executive of Associated General Contractors of Minnesota, an industry group. “This isn’t unlike what the manufacturing, agriculture and mining sectors are facing,” he said.

Still, Worke said the commercial and road construction markets are strong, and prices for materials such as steel, oil and cement are stable. Because of the project’s size, construction firms formed joint ventures to bid on the package. “All of the joint ventures are well qualified,” Worke said.

The lowest bidder was Ames Kraemer SWLRT Joint Venture at $797 million, followed by Lunda/C.S. McCrossan, $808 million; Southwest Rail Constructors, $1.07 billion; and Southwest Transit Constructors, $1.08 billion.

On Monday, the Met Council’s Transportation Committee approved a series of agreements with BNSF Railway and Twin Cities & Western Railroad that will permit light rail and freight rail to share part of the Southwest corridor. The full council will consider the $58.5 million agreement for approval on Wednesday.

The freight talks resulted in an agreement with BNSF that calls for a 10-foot cement wall to span about a mile along the line in Minneapolis, between the Royalston/Farmers Market and Bryn Mawr stations. This angered city officials in Minneapolis, who questioned the wall’s aesthetics and construction.

The rail negotiations needed to be in place before the project applies for a $929 million matching grant from the federal government this fall.

Other transit projects awaiting federal funding are in Maryland, Seattle, Dallas, New York and Santa Ana, Calif.

Another wild card for Southwest involves a federal lawsuit filed by a Minneapolis nonprofit group claiming the project violated environmental laws. A ruling on that case is expected this fall.