A relatively obscure federal agency has been awarded extra time to weigh in on the proposed Southwest Corridor light-rail line.

The Surface Transportation Board has authority over a variety of railroad matters, including abandonment of railroad lines. That could happen if local authorities support re-routing freight traffic from Minneapolis to St. Louis Park to make way for light rail.

The board wants more time to consider a recent environmental report on the impact of different plans for the Southwest Corridor.

"We asked for more time because the ... environmental impact statement was delayed in reaching us," the board said in a statement.

The Federal Transit Administration said it agreed to extend the deadline for written comment on the report from Dec. 11 until the end of the year. The extension also gives the public extra time to file comments.

Construction is scheduled to begin in 2015 on the line from downtown Minneapolis to southwest suburban Eden Prairie. The preferred option of re-routing freight traffic rankled some St. Louis Park residents after the report released in October showed that it would likely cause "severe" noise for hundreds of homeowners. The report attributed some of the noise to "high anticipated speeds" of trains or their "warning signal ... at some stations and crossings."

An alternative route would keep the freight traffic in the Kenwood neighborhood of Minneapolis near the proposed light-rail line.

The board said it didn't know why the environmental report arrived late. A typo misstating the costs of the two alternatives was corrected in late November -- 45 days after the report's release. Hennepin County officials who commissioned the report said the mistake is unrelated to the issues the board might review.

"They're doing their due diligence," County Commissioner Peter McLaughlin said. "I don't think this speaks to the merits in any way."

Pat Doyle • 612-673-4504