Seattle ? The Alaskan Way Viaduct shuttles more than 100,000 automobiles each day on twin concrete decks that soar above the sparkling waterfront. The highway is also drab, rickety and outdated, and Mayor Greg Nickels and his allies want to bury it.

Their proposal to replace the viaduct with a major tunnel has critics pointing to Boston, where another ambitious highway project stampeded past deadlines and cost estimates.

Tunnel supporters dismiss such dire predictions, and believe they could gain a crucial stamp of public approval if the City Council agrees to hold a citywide vote on the tunnel this fall.

Though it’s considered an engineering marvel, the Big Dig has been plagued by cost overruns, delays and faulty construction that culminated in one motorist’s death under a collapsed tunnel ceiling in July.

Nickels’ more modest plan in Seattle would consist of a single tunnel topped by an urban park and commercial zone.