A mail-in election on Tuesday found that the citizens of Seattle support the bored 17.7m diameter tunnel replacing the Alaska Way Viaduct.

The vote concerned one part of an ordinance passed by the City Council in February for agreements on the USD 2bn tunnel project with the Washington State Department of Transportation (WSDOT).

With the voters’ approval on the ordinance (59 per cent), the council is authorised to give notice to proceed beyond preliminary design work.

Design-build contractor Seattle Tunnel Partners (STP) a joint venture of Dragados USA and Tutor Perini, announced last month it will use a 17.7m Hitachi Zosen TBM to excavate the tunnel, which is estimated to be launched in 2013.