I definitely know this until reading this article. Seattle’s bus tunnel will now be a train and bus tunnel. That just sort of blows my mind. Buses and trains will have to line up for the same station platforms. This will be very interesting to see work.
The idea is not totally new for light rail since light rail is often used as surface rail integrated with car traffic. So I guess a tunnel that is shared by trains and buses is not that far-fetched. Photos below are courtesy of the Seattle Times.