Minneapolis park officials will spend up to $500,000 to hire engineering talent they hope will find that a Southwest light-rail tunnel is a reasonable alternative to a new bridge at the Kenilworth channel.

The Park and Recreation Board voted 5-2 Wednesday night to authorize the engineering study in hopes of challenging the project's environmental studies, potentially suing for their alternative.

The board voted after outside attorney Byron Starns told park commissioners that they need to spend more money on engineering expertise rather than lawyers for now. But he assured the board that it is is in a solid position to challenge the proposed Kenilworth bridge if it can show that a tunnel beneath the 101-year-old channel is feasible.

Under federal law, park officials hold a trump card in that they must consent that a federally funded transportation project has only a minimal impact before it can proceed.  The same law authorizes taking parkland only if there's no feasible and prudent alternative.

The studies authorized Wednesday are intended to determine whether a tunnel is technically feasible and to provide a closer estimate of its cost.

The dissenting votes came from commissioners Brad Bourn and Steffanie Musich, who merely wanted the board to follow its usual process of waiting two weeks for public notice for a vote before drawing down $500,000 from its reserves. But park staff argued that haste is necessary to make detailed findings ready when a supplemental environmental impact statement for the project is released early next year.

The board has voiced objections since late 2012 to putting freight and transit rail service and recreational trails on a bridge over the channel dredged in 1913 between Cedar Lake and Lake of the Isles. It has an easement for the channel running under the bridge.

Jennifer Ringgold, a planning supervisor, showed the board drawings of the existing and proposed bridges that showed the width of the crossing growing from 45 to 85 feet. The proposed crossing would actually consist of two bridges, one for freight and the other shared by transit and people using bike and foot trails. There would be a narrow gap between them.

The board voted Sept. 17 to hire outside legal help for $22,000 to evaluate its options for fighting the proposed crossing.  Key officials got a briefing Monday, and met Wednesday with Metro Council officials, while drafting the resolutions to hire engineering help mere hours before the meeting.

A Metro Council e-mail received by the park Superintendent Jayne Miller minutes before the meeting said that completion of the required approval process by cities along the 16-mile route and preliminary engineering set the stage for the required analysis of parkland impacts. But Miller said there was no indication that the council is prepared to do the detailed engineering analysis of the tunnel that the Park Board says is needed to determine if that option is reasonable.

The council said in a statement after the meeting: "The Southwest Project Office has been working with the Park Board for the last two years and is committed to continuing to work with them on the landscape design of the Kenilworth Corridor, the design of the bridge over the channel and the design of the Penn, 21st and West Lake Stations."