The estimated cost of building a connection for passengers to transfer between Metro’s Red Line Bethesda station and the future Purple Line stop nearby has grown by $22.6 million, a Montgomery County official said.

The additional funding to build a mezzanine at a new Metro station entrance would increase the project’s budget by 20 percent. Montgomery has allotted $110.2 million to build a southern entrance to the underground Bethesda Metro station at Wisconsin Avenue and Elm Street, near the western terminus for the street-level Purple Line.

Montgomery is paying for the new Metro station entrance as part of the Maryland Transit Administration’s Purple Line project.

According to the design, Red Line passengers transferring to the Purple Line will head to the southern end of the Bethesda station platform, where an elevator or escalator will take them up to a new mezzanine. They will then use the mezzanine and a short passageway to reach high-speed elevators up to the Purple Line station, which will be in a tunnel beneath a recently built high-rise. Elevators and stairs will connect the Purple Line level to Elm Street above.

That design will allow transferring passengers to avoid about a two-block walk between the Purple Line station at Elm and the Metro station’s northern entrance at East-West Highway. The Bethesda Metro station was built with a “knockout panel” near the arched ceiling that can be removed to allow for a southern entrance.

Maricela Cordova, Montgomery’s manager on the state-run Purple Line project, said the $2.4 million previously allotted to build the mezzanine was a “very, very rough estimate” based on early designs. She said Metro and county officials now believe it will cost $25 million.

Cordova said the county can cover about $5 million of that but is seeking state and federal funding for the remaining $20 million. The final cost, she said, won’t be known until the mezzanine’s construction is put out for bid.

The 16-mile light-rail Purple Line will connect to four Metro stations — Bethesda, Silver Spring, College Park and New Carrollton — but will operate separately from the subway system.

Building the massive elevator shaft and underground passageway at the new southern Metro station entrance is one of the more complex parts of the Purple Line project, which is $250 million over its initial $2 billion construction budget and several years behind schedule.

Maryland officials have said they expect a new lead contractor will resume full construction in the spring. Most Purple Line work stopped in September 2020, when the original construction team quit over delay-related cost disputes with the state.