Sound Transit has come up with a new concept for a downtown Bellevue light-rail tunnel that is shorter and would avoid a costly redesign of the downtown bus center.

The new alternative for the East Link system would include a tunnel that runs up 110th Avenue Northeast instead of 106th Avenue Northeast, the bored-tunnel alternative favored by the Bellevue City Council.

In May, Sound Transit's governing board decided to focus on a street-level light rail route in downtown Bellevue for its environmental studies on the $2.7 billion East Link project. Sound Transit also is doing partial engineering for the bored-tunnel option, which could cost $500 million more.

There is no cost estimate yet for the 110th Avenue tunnel, and the concept still needs to be approved by the Sound Transit governing board. The staff will brief the board on the tunnel at its Oct. 8 meeting and ask whether to add the 110th tunnel to the environmental studies for design work and estimates on cost and ridership, among other issues, said Sound Transit spokesman Bruce Gray.

The 110th alternative would enter near Main Street, run up 110th and then curve east just south of Northeast Sixth Street. From there it would elevate and cross I-405 before heading north to the medical district and a hospital station.

The tunnel would be about 2,000-feet long, versus 5,000 feet for the 106th option and would include a station at Northeast Fourth Street and 110th, within walking distance to the Bellevue Transit Center.

Bellevue Mayor Grant Degginger said he was encouraged that Sound Transit is looking at an option that addresses many of the council's concerns.

"This one certainly seems to have promise, but we have to learn a little more about it," he said. "The devil is always in the details."