District planners have long envisioned how to redesign K Street NW — one of the city’s premier business addresses — from a sea of traffic to an iconic boulevard where buses breeze through the downtown of the nation’s capital on their own transitway.

In addition to making the thoroughfare more transit-friendly, planners have wanted to scrap K Street’s decades-old side service roads — believed to be among the only ones in the city — which, they say, confuse motorists, clog traffic and often leave pedestrians and cyclists scrambling between medians.

After 15 years of studies and reports, the proposed K Street Transitway project suddenly looks like it might get beyond the drawing board. D.C. Mayor Muriel E. Bowser (D) has included $122 million in her capital budget to finish the project’s design and build it, potentially beginning construction in 2023 and opening in 2025.

“We are concerned about congestion across the city,” Bowser told the D.C. Council during her budget presentation Wednesday. “I put it among the things that can stifle the growth of the District of Columbia. The investments we make in public transit are first and foremost in my mind on how we move more cars off the road.”

The mayor’s other transportation spending priorities include $10 million for 18 Capital Bikeshare stations and $2.8 million to hire 40 traffic-enforcement officers to protect pedestrians and enforce bike-lane laws. She also has proposed $3.1 million to subsidize Circulator bus service by making the service free on all routes and $13 million to expand the Circulator into Ward 7 in Southeast.

None of the proposals are a done deal. The D.C. Council has final say on the budget, which it must pass by the end of May. However, several lawmakers have praised the mayor for trying to fund the project.

Under the transit plan, K Street would be redesigned between Ninth and 21st streets NW. Two dedicated bus lanes — one in each direction — would run down the middle and be separated from traffic by raised medians that would have room for passenger waiting areas. The outside service lanes would disappear. Instead, three lanes of traffic would remain in each direction along both sides of the transitway, but the third lanes could be used for parking during off-peak hours.

The idea, planners say, is to make buses more attractive and reliable by keeping them out of backups. The new design, they say, also would use the road space more efficiently and make it safer for pedestrians and cyclists. The transitway would have enough room to potentially convert to street cars in the future.

In the budget proposal, the District Department of Transportation would seek environmental approvals this year, start the final design in 2021 and begin construction in 2023. K Street would remain open during the roughly two years of construction, city officials said. Bowser also has said she would like to find a way to open a busway within four years.

The city has studied the idea since 2005 and chose an alignment in 2009, but the project has not been funded beyond 30 percent design.

“The roadway was really designed for vehicle throughput,” said DDOT Director Jeff Marootian. “We want to make sure it’s safer, more efficient and less confusing for everyone who’s using it.”

Beyond connecting Georgetown on the west and Capitol Hill on the east, K Street NW has long been considered the epicenter of D.C.’s business district and a power address for lobbying and law firms, companies, restaurants and shops. Even so, it has fallen short of its potential as “a great transit corridor and a grand civic space,” according to a panel of urban-planning and transportation experts who studied the corridor in 2004.

“A reconstituted K Street should be recognized as a great and beautiful street that rivals major downtown corridors throughout the world, such as Fifth Avenue in New York and Michigan Avenue in Chicago,” wrote the panel convened by the National Capital Planning Commission and the Downtown D.C. Business Improvement District.

In addition to a transitway, the panel said, wider sidewalks to accommodate outdoor dining, and more mature landscaping and trees, would make the area more inviting and “parklike.”

The street’s service roads, the panel said, were added before the 1950s, “during an era when automobiles were glamorized.”

Since then, experts say, the increase in bus riders, cyclists, pedestrians and delivery and ride-share vehicles have vastly changed how streets must function.

DDOT officials say buses — K Street alone can see up to 55 per hour during peak times — carry about 40,000 people through downtown on K, I and H streets.

Leona Agouridis, executive director of the Golden Triangle Business Improvement District, said east-west travel has always been difficult through the downtown area, especially since part of Pennsylvania Avenue NW was closed to vehicles in front of the White House after the Oklahoma City bombing in 1995.

“This is a big step toward a better K Street, more in line with its truly iconic and symbolic qualities,” Agouridis said. “It should be a grand boulevard, not a parking lot.”

Several commuters heading home on K Street one recent evening said they would welcome a redesign, especially if it meant fewer traffic backups and more reliable bus service.

Trevor Bruce, an administrative assistant, said it is time to get rid of the service lanes, where he often sees traffic snarled behind motorists trying to swerve into and out of the regular lanes. He said he also sees pedestrians who cross the service lanes on do-not-walk signals becoming stranded on medians.

“I don’t think it’s too pretty to look at now . . . so any change would be good,” Bruce said. “The street is in bad shape, and there’s always heavy traffic, especially in the service roads.”

Geoff Hainbach, an attorney, said he’d be “all for” a transitway that would make buses more reliable. Now, he said, they can be 10 to 15 minutes off schedule.

“During rush hour, you see the expected time of arrival get pushed back,” Hainbach said, pointing to the digital display at his K Street bus stop. “It gets annoying because it’s hard to plan how long it’s going to take.”

Some motorists say they are worried they will lose out. Yema Morgan, who drives to stunt-rigging jobs around the city, said she’s concerned about K Street being ripped up for construction — “That sounds like a nightmare scenario,” she said — and the possibility of losing any street parking, which is already in short supply.

“People do drive,” Morgan said, pointing to a line of cars slogging through the evening rush. “Look at this.”

Fenit Nirappil contributed to this report.