Montgomery County Executive Marc Elrich (D) has included no money in his capital budget proposal for the county’s long-promised plan to build a tunnel to carry cyclists and runners on the Capital Crescent Trail beneath busy Wisconsin Avenue in downtown Bethesda.

County officials say the project’s construction costs have ballooned, making it too expensive to include in a tight budget.

The move, which will at least delay the project, has angered cyclists and trail advocates who say Montgomery officials are breaking a public promise to have a trail tunnel completed by the time the Purple Line opens.

The tunnel, which would be adjacent to a future Purple Line station, would be paid for by the county but built alongside the state’s light-rail project. The opening of the Purple Line in Montgomery County is scheduled for mid-2023, after the line begins operating in Prince George’s County in late 2022, Maryland transit officials have said.

Requiring cyclists, walkers and runners to cross six-lane Wisconsin Avenue will make the trail more dangerous, less convenient and less appealing, particularly for those with children and others looking for a “low-stress” walk or ride, advocates say.

The tunnel “is something Montgomery has been saying for years is going to be done,” said Colin Browne, a spokesman for the Washington Area Bicyclist Association. “It puts a big hole in the trail for however many years it takes to build it.”

But county officials say early design work put the projected construction cost at more than $50 million — far more than the $25 million initially anticipated — in part because the tunnel would have to be longer than expected because of the constraints of surrounding streets.

The county’s capital budget is already tight, county officials said. Adding money for a trail tunnel “would be challenging” because of the need to pay for projects already under construction and for repairs needed immediately on roads, bridges and other infrastructure, said Chris Conklin, director of Montgomery’s Transportation Department.

Conklin said the county has budgeted money to build a surface trail that, heading west, will follow 47th Street at Elm Street Park, cross Wisconsin at the light and proceed along Bethesda Avenue before joining the rest of the trail across Woodmont Avenue. The surface trail is to open this year, Conklin said.

“It will provide an immediate, safe surface crossing of Wisconsin Avenue,” Conklin said.

He said county officials can reexamine the tunnel option after its construction costs are refined and they see how well the new surface trail works.

“We were not prepared for all these costs when the project was discussed,” said county spokesman Neil Greenberger. “There’s no money in this [capital budget], but we’re aware of it and aware of its importance to the community. We can do it later.”

Montgomery County Council member Hans Riemer (D-At Large) said he will try to put the money in the budget but would need to find other projects to cut.

Requiring trail users to cross Wisconsin at a light, Riemer said, “is sort of like putting a stoplight on the Beltway. We just don’t want to create that kind of disruption if we can avoid it.”

Trail advocates say the segment in downtown Bethesda is a key link in the Washington region’s trail network. The Capital Crescent Trail will connect Georgetown in Northwest Washington to downtown Silver Spring. Once completed, the Metropolitan Branch Trail will connect downtown Silver Spring with Union Station in the District.

County Council member Andrew Friedson (D-District 1) said he also will look for ways to include the tunnel funding.

“We made a commitment as a county to build the tunnel, and a commitment should be kept,” Friedson said. “It’s a key part of the Purple Line project and why many people supported it. … It’s not just a recreational trail. It’s a central part of our transportation infrastructure.”