The state Department of Transportation broke ground Wednesday on a project that will open a new eastbound HOV lane on I-90 between Bellevue and Mercer Island in preparation for East Link light rail.

The $31-million project will free existing center express lanes for eventual light rail use.

The center lanes – which operate westbound in the morning and eastbound at night – will remain open to express HOV traffic until construction begins on the East Link light-rail line.

State transportation officials expect the new eastbound lane to be open in mid-2012, with East Link construction beginning by early 2014.

Wednesday’s groundbreaking ceremony launched the second part of a three-stage plan to increase capacity on I-90 and pave the way for light rail.

The first phase, which cost $34 million, included the October 2008 opening of a new westbound HOV lane on I-90 between Bellevue and Mercer Island.

Both of the first two phases add new direct-access HOV ramps at Bellevue Way SE and 80th Ave. SE.

Stage three will involve new HOV lanes in both directions between Mercer Island and Seattle.

The total cost for all three phases is estimated at $188 million.