Mayor Mike McGinn announced this afternoon that the Seattle City Council and the city's department of transportation have chosen the local office of San Francisco-based Nelson/Nygaard to review SR 520 design options, including the feasibility of light rail on the bridge.

Previously, council transportation chair Tom Rasmussen told me today, the city planned to direct the consultant to look only at "issues like mitigation, protection of the Arboretum, and how transit works" with the bridge. That contract, he said, would have cost the city around $100,000.

With the addition of light rail to the consultant's scope of work, McGinn said, the contract will cost the city around $250,000, to be paid for jointly by SDOT and the city council.

"Yesterday, the city council said they wanted to look at how the city could become carbon neutral," McGinn said, referring to the council's announcement of its 2010 priorities. To do that, he said, "we need to transform our transportation system."

The consultant will wrap up its work by April 15, the same day the public-comment period for the 520 replacement options ends.

McGinn said his proposal could be completed more quickly than the state's preferred "A+" option (four general-purpose lanes, two HOV) because of public opposition to that option and because the bridge replacement isn't fully funded. "If we can come up with an option that has strong public support and that is fully funded, we believe it could be completed sooner," McGinn said.