Noise from future Southwest Corridor light-rail trains is likely to be "severe" for hundreds of homeowners, but the benefits of transit ridership outweigh environmental problems, concludes a report released Friday.

The long-awaited report on the environmental impact of the proposed transit line between Minneapolis and Eden Prairie says it would result in "modest improvements to air quality" and also help the economy.

Supporters of the light-rail line welcomed the draft report as a necessary step toward gaining federal funding for the $1.25 billion project.

"It's a major milestone," said Hennepin County Commissioner Gail Dorfman.

The report details hurdles that need to be cleared for the project to move forward. It shows 201 parcels of land where residents would experience potentially severe noise if the preferred route for the line is adopted.

It attributes some of the noise to "high anticipated speeds" of light-rail trains or their "warning signal ... at some stations and crossings."

Much of the impact would be in St. Louis Park, caused by re-routing freight trains to make way for a portion of the light-rail line. Moving freight traffic to St. Louis Park would cause "severe noise impacts ... due to the freight locomotive horn noise" at highway crossings.

Nearly 500 residential units also would experience significant vibration, the study said.

"What are we going to do to minimize the noise and vibration?" asked Dorfman, a former St. Louis Park mayor. "We will take the freight as long as there is adequate mitigation for the impacts."

Hennepin County Commissioner Peter McLaughlin, another supporter, said the draft "represents a big step forward ... the issues will get the scrutiny they deserve."

Buy land, reroute trains

The report anticipates buying 125 parcels of land to make way for the line, expected to open in 2018 and run 15 miles from downtown Minneapolis to the southwest suburbs.

Preliminary engineering work is expected to occur early next year.

Public hearings on the draft environmental study will be held Nov. 13 at Hennepin County Government Center, Nov. 14 at St. Louis Park City Hall and Nov. 29 at Eden Prairie City Hall. Comments will be accepted through Dec. 11 before a final report is adopted.

In endorsing the route preferred by government officials, the study rejected several alternative routes and the option of not building a light-rail line in the southwest metro.

"The overall benefits -- including increased transit ridership and enhanced mobility -- outweigh the potential adverse environmental impacts," the report said.

One benefit of the preferred route is that it would allow freight trains "a safe, efficient and economical connection to St. Paul."

The Federal Transit Administration, in granting approval for preliminary engineering on the project, insisted that proponents consider the environmental impact and cost of rerouting the freight railroad. Backers are counting on the federal government to pay for half the cost of the project.

A decision on rerouting freight trains is up to the Metropolitan Council, the regional planning agency. The agency said Friday that it expected to take up the issue in 2013.

"Staff of Met Council have initiated conversations, but no negotiations, with the freight railroads in the Southwest LRT corridor -- Canadian Pacific Railway, BNSF and Twin Cities & Western Railroad," spokeswoman Laura Baenen said in a statement Friday.

Public comments to the draft environmental study and preliminary engineering next year will help shape decisions, she said.

Pat Doyle • 612-673-4504