A rendering shows a proposed bike line on Louisiana Avenue near Union Station. (DDOT)

In its effort to expand the city’s network of bike lanes, the District has encountered many roadblocks, from neighbors opposing the removal of curbside parking to drivers clamoring to keep their travel lanes.

And then, there’s Congress — literally standing in the way of one bike path.

More than three years after it was proposed, a 0.6-mile cycle track on Louisiana Avenue between Union Station and the U.S. Capitol awaits a green light from the Hill.

The problem? Louisiana Avenue, though it looks like a city street, is actually owned by the Architect of the Capitol, the steward of the Capitol grounds, and major fixes go through that office.

“Here we have a road that is a very local road . . . and the people who get to make all the decisions are coming here from all over the United States,” said Garrett Hennigan, a community organizer with the Washington Area Bicyclist Association who has been lobbying for the bike lane since 2015. “This is exactly why statehood is such a frustrating issue for us local folks.”

Federal officials say they support a bike-lane concept proposed by the District Department of Transportation, but they have some reservations that are stalling progress: Chiefly, the Senate sergeant at arms, who manages the Senate parking supply, isn’t thrilled about giving up diagonal parking used by Senate staffers in the easternmost block of the road.

A proposed bike lane on Louisiana Avenue, between Massachusetts Avenue and North Capitol Street near the Capitol and Union Station, could displace the 37 parking spots shown in the center, which are used by Senate staffers. The Architect of the Capitol owns Louisiana Avenue and is asking the city to preserve the parking space if it wants to build the bike path. (Luz Lazo/The Washington Post)

“As with most things,” Hennigan said. “It comes down to parking.”

Thirty-seven parking spaces, to be exact. The road is only 0.4 miles long stretching from Constitution Avenue NW at the foot of the Capitol to Columbus Circle NE across from Union Station.

“We think there’s a much better use of that public space, which is making that street more accessible for more people,” Hennigan said.

But keeping the parking is turning out to be the dealbreaker to get the project going. In a Sept. 14 letter to DDOT, Architect of the Capitol Stephen T. Ayers listed eight concerns that must be resolved before the city can move forward with the final design, among them to retain the parking spaces “to the greatest extent possible.”

Parking is a high-demand commodity in the nation’s capital and is at the center of many of the city’s street debates. On Capitol Hill, doing without those three dozen parking spots, isn’t a choice Senate Sergeant at Arms and Doorkeeper Michael C. Stenger wants to make — especially with a renovation of a Senate parking facility in the works, officials familiar with the negotiations say.

Questions to the office of the Senate sergeant at arms about its parking concerns were referred to the Architect of the Capitol. The Architect’s spokeswoman, Erin Courtney, did not respond to parking questions but said the agency is supportive of a bike-friendly Capitol Hill and looks “forward to continuing to work with DDOT on this initiative.”

In his letter to DDOT, Ayers said while the DDOT concept is satisfactory to allow the agency to formally begin the design phase, unresolved issues must be addressed.

Among the demands: a better connection at Columbus Circle to link to the Metropolitan Branch Trail and modifications to the left turn lanes at New Jersey Avenue and North Capitol Street. DDOT must ensure that the project meets the needs of the U.S. Capitol Police and that the cycle track barrier is removable to support events such as the presidential inauguration parade.

Sam Zimbabwe, chief project delivery officer for DDOT, said the agency is advancing the detail design for the project and working on answers to concerns spelled out in Ayers’s letter before requesting final permission.

A conceptual design for the bike lane puts it in the middle of Louisiana Avenue, an option that officials say not only provides the best cycling connectivity but also has fewer traffic impacts, does not affect bus operations and preserves the most parking.

This option would require moving the electrical lines to put new signals closer to the median. As part of the project, the city is also set to improve the bike connection with the First Street bike lane.

Ultimately, city officials said, the bike lane may end at North Capitol Street instead of going all the way to Columbus Circle, leaving that last block closer to Union Station untouched to preserve the median parking available to the Senate.

If and when Ayers gives the project the green light, it will then need to be approved by the Senate Rules Committee and the House Office Building Commission, D.C. Del. Eleanor Holmes Norton (D) said.

“The Senate and the House committees are not going to do anything until we get to the formal design plan and we are nowhere near that now,” said Norton, the District’s nonvoting member of Congress. She has urged federal officials to move on the bike lane, saying that losing a few parking spaces is only a “a small price to pay to ensure public safety and help alleviate congestion near the Capitol.” Besides, she said, the bike lane has wide support, even from members of Congress.

“They are moving very, very slowly,” Norton said. “This is not a city street, but it’s in our city and it messes our city up by not being able to add the bike lane.”

The proposed bike lane is a missing piece in the region’s bike network. It would link the Metropolitan Branch Trail, a major bike route from south of Fort Totten to Union Station with the Pennsylvania Avenue Cycle Track, one of the city’s busiest bike paths connecting other major bike corridors such as 15th and M streets NW.

The project is one of about a dozen the city is counting on to double its 10 miles of protected lanes by 2024. City elected officials say the bike lane is critical to ensure the safety of cyclists and reduce traffic. The Congressional Bike Caucus, a group of more than 130 lawmakers, supports the project. More than 650 residents have signed a petition calling for the path to be moved forward, while advocates say the project is more critical than ever to address the growing number of people in the region who are getting around on two wheels — whether that’s bicycles or electric scooters.

City transportation officials recall two other instances in recent years where they sought a permit from the Architect of the Capitol to build new bike facilities. Both cases involved minor changes to the roadway, such as repainting. But the city frequently works with federal agencies on roads or other issues. The National Park Service, for example, has jurisdiction of streets on the Mall.

Zimbabwe said construction is unlikely in 2019, but he anticipates a plan that the Capitol agrees with this year.

“We will work with them on whatever steps are necessary to keep this project going,” he said.