In a small win for Seattle Mayor Greg Nickels, the state Wednesday asked outside experts to study the mayor's proposal for a four-lane Alaskan...

In a small win for Seattle Mayor Greg Nickels, the state Wednesday asked outside experts to study the mayor’s proposal for a four-lane Alaskan Way tunnel.

Gov. Christine Gregoire and state legislative leaders gave the project’s expert review panel a Feb. 13 deadline — about a week before ballots are sent to Seattle residents for an all-mail advisory vote. Ballots must be postmarked by March 13 to be counted.

Voters face two questions: yes or no on a four-lane tunnel — smaller than the six-lane version Nickels and the state originally proposed — and yes or no on a six-lane elevated replacement for the aging Alaskan Way Viaduct.

City officials, the expert panel and a state project team examined the four-lane-tunnel idea for a week in January. The panel said the idea “shows promise,” but the state stopped the inquiry. Nickels asked for studies to resume.

Now, state leaders are seeking the panel’s views about whether a four-lane version would really slash the bigger tunnel’s $4.6 billion price down to $3.4 billion, as the city contends, and whether it’s safe to use the shoulders of a four-lane highway as exit lanes to boost capacity at rush hour, as the city suggests.

Gregoire’s staffers would not discuss whether she will seriously consider a four-lane tunnel.

“This is about responsibility to the voters, so they can make a decision,” spokeswoman Holly Armstrong said.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com