What next, Battery Street Tunnel, you narrow, sepia-toned relic of yesteryear?

What will happen to the Battery Street tunnel after the viaduct comes down?

This is a question KUOW has received multiple times as the new Highway 99 tunnel, built to replace the aging Alaskan Way Viaduct, inches closer to completion.

This has been settled by the City Council and –to the disappointment of community members who wanted to repurpose the space – the answer is that it will be shut down and filled in with rubble.

Why, you might ask, would the city shut down a perfectly good piece of infrastructure like this?

Listener Stephen Growdon was curious about this. He wrote, “As a Seattle resident who frequently drives through the Battery Street Tunnel, I am curious about this soon-to-be-obsolete feature of our city. I consider the tunnel to be ugly, but highly functional — like a lot of things built in the 1950s. Filling in the tunnel with ruble seems to be a waste of this public asset.”

Others felt the same and had suggestions for the tunnel’s reincarnation: a park, an underground farm, a space for Metro buses, and a waste water treatment plant.

But city and state officials say this thoroughfare under Battery Street – with its dim fluorescent lighting, reminiscent of a poorly lit hospital ward – is not actually a perfectly good piece of infrastructure at all. They say it’s old and would likely fail in the event of a big earthquake.

Jon Layzer, of the Seattle Department of Transportation, told the City Council earlier this year that they’ve explored options for re-using the tunnel. He said it would be too expensive to bring the space up to code.

"We've looked at general or specific uses of the tunnel, and in each of those exercises, we've found that adaptive re-use of the tunnel would cost on the order of $100 million," Layzer said.

Supporters of revamping the tunnel said they believed the cost to bring it up to code could be much lower.

In March they asked the Council to delay their final decision on what to do with the space until re-use options could be explored further.

But the decision was made to go ahead with a plan that will see state contractors fill the passage with rubble when the Alaskan Way Viaduct is demolished.

With that decision made, listener Stephen Growdon had another question:

“I’m curious if buildings located above the tunnel will be able dig deeper basements, parking garages or other subterranean structures once the tunnel is decommissioned and filled in? Also, will closing down the old tunnel free up land for development above the tunnel?”

Again, the answer is no, Stephen. The tunnel runs under a street that won’t have buildings or developments above it.

“Once the tunnel is decommissioned, the area on top of the tunnel will continue to be used for transportation purposes,” said spokesman Norm Mah of the Seattle transportation department.

So what happens now?

The Washington State Department of Transportation will soon choose a contractor to dismantle the viaduct, decommission the tunnel and reconnect north surface streets. The contractor will decide how to do these projects, including how to fill the tunnel. The state wants the contractor to do a range of things to shut down the tunnel, including cleaning soot from the inside before it’s filled.

Once the tunnel is filled, a triangular piece of land at one end will be handed to the city and could be turned into a park, a community space or possibly even housing. That decision has yet to be made.