Outside experts say that if the state wants to solve political congestion, transportation officials should quit treating the Alaskan Way...

Outside experts say that if the state wants to solve political congestion, transportation officials should quit treating the Alaskan Way waterfront corridor like a freeway.

The state could allow lower speed limits, so that a narrow tunnel or viaduct could operate safely — and be built at a much cheaper cost, says the panel of experts.

The eight-person panel, appointed last year by the state to study the Alaskan Way Viaduct and Highway 520 replacement projects, aired its views Friday in a letter to Gov. Christine Gregoire.

On Feb. 13, Gregoire endorsed a six-lane, $2.8 billion elevated highway, and discarded a four-lane, $3.4 billion tunnel alternative — after state Transportation Secretary Doug MacDonald declared it unsafe.

Seattle Mayor Greg Nickels is trying to save his recent tunnel proposal, in which the safety shoulders of a four-lane tunnel become exit lanes at rush hour. To compensate for the tighter space, city transportation managers suggest a 35 mph speed limit whenever cars are traveling on the shoulder.

David Dye, DOT urban corridors administrator, has said it makes no sense to spend more than $3 billion on a project that would limit capacity to handle future traffic on Highway 99.

“It is not unusual for persons within the engineering community to have differences of opinion. This seems to be one of those cases,” Dye said Friday night.

National standards call for 10-foot shoulders, but narrower shoulders have been used where space is limited.

The panel said many such projects “are operating safely, provide necessary capacity and are integrated with the surrounding environment. This is certainly worth further review by everyone involved in the project.”

The city hopes its plan, called “Tunnel Lite” by some, will make tunneling more affordable than an earlier $4.6 billion, six-lane design for higher speeds.

The latest tunnel concept was studied by the state’s viaduct project team for only four days in January, but engineers produced several hundred pages of drawings, charts and calculations, and an optimistic — but inconclusive — summary report. The panel then said it “shows promise.”

Since then, some members said in interviews the proposal deserves a closer look.

A citywide advisory vote is now under way, in which citizens choose a viaduct or a tunnel, or say no or yes to both. Ballots for the mail-in election must be postmarked by March 13.

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