The Montgomery County Council tentatively approved $54.9 million on Thursday to build a tunnel to carry cyclists and runners on the Capital Crescent Trail beneath Wisconsin Avenue in downtown Bethesda.

The tunnel will be separate from, but adjacent to, the Bethesda station for the 16-mile light-rail Purple Line now under construction. It will carry trail users between Woodmont Avenue and the eastern side of Wisconsin Avenue, where the trail will run along the Purple Line tracks toward downtown Silver Spring.

The tunnel is scheduled to open in 2026 — three years after the Purple Line’s scheduled opening in Montgomery. County officials had previously promised that the trail tunnel would open at the same time as the light-rail line. However, council staff said it needed to be pushed back to the later years of the county’s six-year capital budget, much of which is needed for school construction.

The council approved the tunnel funding unanimously in a straw vote. The final vote on the county’s capital and operating budgets is expected May 21.

Council members rejected a shorter tunnel. At an estimated cost of $46.9 million, it would have been less expensive but also would have had less head room and would have required trail users to cross 47th Street, just east of Wisconsin.

Several members said the trail was one of the busiest in Maryland, if not the country, and worth investing in as an important piece of transportation infrastructure. Building a tunnel beneath Wisconsin Avenue, they said, also would jibe with the county’s efforts to make walking and cycling safer.

“I think coming with a less-than-full option — I think we’re just going to regret it,” said council member Hans Riemer (D-At Large).

Council member Andrew Friedson (D-District 1), whose district includes downtown Bethesda, said the less expensive option would result in a trail too steep for children and seniors.

“This is going to be the infrastructure we have in our community to connect east and west for decades and decades to come,” Friedson said.

Cycling groups and trail advocates had criticized what they feared was the loss of a trail tunnel in January, when Montgomery County Executive Marc Elrich (D) didn’t include funding for it in his budget proposal. An Elrich spokesman said that the county executive appreciated the trail tunnel’s importance to the community but that the county couldn’t afford it after its cost had more than doubled during more detailed engineering.

Trail advocates and cycling groups said county officials had long promised a trail beneath Wisconsin as part of getting community buy-in on the Purple Line.

Requiring cyclists, walkers and runners to cross Wisconsin, they said, would 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.

The approved tunnel will be 1,000 feet long and contain a 12-foot-wide trail with two-foot shoulders on either side. It also will have lighting, security cameras and emergency phones, according to the county plan.

Trail advocates say the segment in downtown Bethesda is a key link in the Washington region’s trail network. After it is rebuilt along the Purple Line, 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.

This summer, a new surface trail is scheduled to open in downtown Bethesda. County officials say trail users will have an improved crossing at Wisconsin near Elm Street Park and a separated path along 47th Street, Willow Lane and Bethesda Avenue, where it will join the Capital Crescent Trail at Woodmont Avenue.