SEATTLE -- The Washington State Department of Transportation issued a report on Tuesday saying the option for a four-lane tunnel to replace the Alaskan Way Viaduct is "unacceptable."

A letter from Transportation Secretary Doug MacDonald to Gov. Chris Gregoire said the so-called "surface/tunnel hybrid proposal falls short of meeting basic safety and design standards" because there are only four full-time traffic lanes. The replacement for the existing six-lane viaduct "has to include six lanes and shoulders to maintain safety and capacity," the letter said.

The mayor's proposal for a four-lane tunnel would allow traffic on the shoulders during the morning and evening commutes.

WSDOT said Seattle's proposal, also known as "tunnel lite," should be dropped from further consideration. The city had hoped it would save money and still achieve Seattle Mayor Greg Nickel's goal of opening downtown waterfront views.

The state is pushing to replace the 54-year-old viaduct with a new elevated highway that could handle more than 100,000 vehicles a day and withstand an earthquake.

Voters in Seattle will cast mail-in ballots by March 13 in an advisory vote. The options included in the ballot measure are a four-lane tunnel or a new viaduct.