Susan Hutchison's call to put light rail on SR-520 instead of I-90 is as cunning as it is potentially ruinous for the prospect of expanding light rail throughout the region:

Injecting a new theme into the race for King County executive, Susan Hutchison proposed Tuesday that Sound Transit move its planned light-rail line across Lake Washington from Interstate 90 to a new Highway 520 bridge.

Seattle Transit Blog contributor (and all around transit nerd) Ben Schiendelman wrote a post last year in which he describes, in ridiculous detail, exactly why building light rail on SR-520 would be a big mistake. It's pretty technical, but for some really good public policy reasons, crossing I-90 is the way to go.

Enter Susan Hutchison, Transportation Expert:

"There's no reason to take lanes out of I-90, which is the major commuting road from the Eastside to Seattle, and turn it over to light rail," Hutchison said in a televised debate with her opponent, Dow Constantine. The matchup was co-sponsored by KING-5 and The Seattle Times.

Hutchison said a priority in transportation planning should be to reduce auto congestion, and said after the debate, "I don't think the voters care which route it takes, but people are upset about losing lanes on I-90."

Since Hutchison's anti-rail backers can't beat light rail at the polls, they're backing her instead. If Hutchison wins, she'll have a big impact on transit policy in King County, and a big push to move light rail from I-90 to SR-520 could really muck up the works, as Ben explains:

A 520 crossing would also impose any delays attached to construction of the new SR-520 bridge on Sound Transit’s schedule. The risk added by working with WSDOT on the project would likely also make Sound Transit less competitive for Federal Transit Administration grants.

By favoring SR-520 over I-90, Hutchison still gets to claim that she's pro-transit, while her backers get a shot at derailing the whole project.