(CHICAGO, AP) — Illinois and the federal government have approved an environmental impact statement for the high-speed rail line under construction between Chicago and St. Louis.

The review is an important step because it identifies a route through Springfield that would end a dispute that had threatened to hold up the project.

It also recommends a route around some of the congested tangle of rail lines between Chicago and suburban Joliet. Upgrades to that suggested corridor would be $500 million cheaper than the existing route because fewer overpasses would be needed.

The assessment also clears the way for possibly building a dedicated line in the future so passenger trains wouldn’t have to share track with freight trains.

Upgrades for 110-mph service over most of the line should be finished by 2015.