The Seattle City Council's transportation committee approved legislation Thursday to fill in the Battery Street Tunnel and keep its planned decommissioning on track.

It came after the Seattle and Washington state departments of transportation both expressed concern about slowing down the timeline amidst renewed calls to preserve the tunnel which was built in the early 1950s.

Recharge the Battery, a volunteer, citizen-led organization, has been pushing the city to slow down the process so it can further explore reuse off the site.

The tunnel currently connects the Alaskan Way Viaduct and Highway 99 through Belltown and under Battery Street. It has long been targeted to be filled once the new waterfront tunnel opens later this year.

The citizen group believes it could be used as a public park, museum, or even a bus and bike bypass.

However, Seattle Department of Transportation Major Projects Director Jon Layzer told the committee that the tunnel is a "failing structure" which supports not only Battery Street, but the adjoining properties. It is also filled with vital electric and sewer connections. He says SDOT has examined the issue multiple times and has determined it would cost upwards of $100 million to preserve it for public use -- money the state nor city has available.

With that said, the committee approved moving the legislation forward for a full council vote later this month.

A WSDOT spokesperson also told the council the new waterfront tunnel should open later this year, but only after some traffic headaches. WSDOT says there will be a three-week closure to allow for work crews to transition from the viaduct to the tunnel. After the new tunnel opens, the viaduct will be torn down starting in 2019 and the Battery Street Tunnel will be filled around the same time.