The Start of Sound Transit's University Link Has Me Thinking About Tunnel Ventilation in Seattle

Yesterday Senator Patty Murray ran a bottle of champagne down a zipline to christen a pair of tunnel digging machines that will be working next to each other to dig southbound and northbound tunnels under Capitol Hill to connect the University of Washington with Capitol Hill and Westlake Center,

This will be Sound Transit's University Link of the ever growing Puget Sound light rail system.

University Link will cost around $2 billion. The tunnel part of the link is two miles long. The tunneling phase will last 14 to 18 months, with the link scheduled to be completed in 2016.

Soon the Alaskan Way Viaduct replacement tunneling will begin. Seattle has a lot of tunneling going on.

All this tunneling had me thinking back to when the downtown Seattle Transit Tunnel was built back in the 1990s. That tunnel was built with future rail in mind. But, they got the rails wrong and that had to be re-done. The buses that run in the Seattle Transit Tunnel have to be dual buses. Meaning they run on both diesel and electricity. This makes for very expensive buses.

To enter the tunnel a bus has to stop and attach the electric power from a line over head.

I remembering wondering at the time the transit tunnel was built why a ventilation system was not doable, rather than having to have dual powered buses.

Now I'm really wondering about this, due to the Alaskan Way Viaduct replacement tunnel. Vehicles entering that tunnel will not be required to be dual powered vehicles. The Viaduct replacement tunnel is deeper than the Seattle Transit Tunnel.

So, how is the Alaskan Way Viaduct replacement tunnel to be ventilated? It seems like a tunnel with cars running through it is going to generate a lot more to ventilate than buses running through a tunnel.

The need for the dual buses in the Seattle Transit Tunnel, rather than ventilation, has perplexed me for almost 20 years. And now it perplexes me more than ever.