was any proposal put forth for constructing a bus tunnel?
Yes, a downtown bus tunnel.
Downtown Seattle Transit Tunnel
The concept of a downtown bus tunnel was first proposed in 1974 during discussions between Governor Dan Evans and Seattle Mayor Wes Uhlman about regional transportation projects in response to the proposed extension of Interstate 90 into Seattle via a third floating bridge crossing Lake Washington. 
where is downtown seattle transit tunnel? Seattle, Washington, United States who built it? UNANSWERABLE which are the different stations that the tunnel connects to? Westlake and International District/Chinatown stations does it also connect to any route? Yes, it connect bus routes. how does the transit run? The OCC controls vehicle movements by using on-board radio-frequency identification tags installed on tunnel buses and light rail vehicles, their locations tracked by passing over induction loops embedded in the tunnel roadway. were there any proposals made to make a subway ealier? Yes, there were several proposals for a cut-and-cover subway tunnel. were any of them approved? Yes, a proposal as part of the Forward Thrust initiatives was approved. can you tell me something more about the thrust? They were a series of bond propositions put to the voters of King County. when was the proposal approved by them? 1968
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Downtown Seattle Transit Tunnel [SEP] Bus tunnel proposal and approval
The concept of a downtown bus tunnel was first proposed in 1974 during discussions between Governor Dan Evans and Seattle Mayor Wes Uhlman about regional transportation projects in response to the proposed extension of Interstate 90 into Seattle via a third floating bridge crossing Lake Washington. Metro Transit later commissioned a study into the bus tunnel, released the following July, which determined that it would not be able to adequately meet the rush hour demand of downtown bus ridership by 1980. The study suggested that a double-decked tunnel with automated guideway transit to complement bus service, running from Union Station to the Seattle Center, would be able to meet projected demand at an estimated cost of $450 million.