Early in Mayor Eric Adams’s first term, he rode a B41 bus through Brooklyn to cement his commitment to speed up New York City’s notoriously slow buses, part of his campaign pledge to be an advocate for bus riders and bicyclists.

Bus riders thought they had their champion. A riders group presented Mr. Adams that day with a jacket that read “N.Y.C. Bus Mayor” across the back and celebrated his vow to create 150 miles of new dedicated bus lanes in four years.

Then politics interfered.

The city, which has the slowest buses in the nation — averaging eight miles per hour — is expected to add as few as 10 miles of bus lanes this year. In 2022, Mr. Adams’s first year as mayor, just shy of a dozen miles were added.

The Adams administration is drawing up plans for new bus lanes on half a dozen more routes, including a three-mile proposal for a busy corridor along Fordham Road in the Bronx. More commuters rely on the bus in the Bronx, per capita, than in any other borough, and 60 percent of households do not own a car, according to analyses of Census Bureau data by city agencies.

But now that plan seems in limbo, after local businesses objected and one of the mayor’s political allies, Representative Adriano Espaillat, raised doubts.

Richard Davey, the president of New York City Transit who oversees the city’s vast subway and bus system, said in an interview that Mr. Adams had been a “huge transit mayor for us,” citing the mayor’s focus on subway crime and support for discount MetroCards for poor New Yorkers.

But the Metropolitan Transportation Authority is powerless to speed up its buses unless the city creates more bus lanes.

“The math won’t add up by the end of the mayor’s four years,” Mr. Davey said on Monday as he rode a Bx36 bus through the Bronx.

Transit advocates worry that other bus-friendly proposals could be in jeopardy, such as a major bus-lane plan for Flatbush Avenue in Brooklyn that travels through the heart of neighborhoods that Mr. Adams won in 2021. Rita Joseph, the councilwoman who represents Flatbush, said that she supports bringing a bus lane to her district.

“I have heard from my neighbors — both for and against, and now as an elected leader it is my responsibility to work with my colleagues to find a compromise that everyone can agree on,” Ms. Joseph said in a statement.

With New York City mired in traffic gridlock and grappling with the impact of climate change, giving priority to buses seems an obvious solution. London and Beijing have sped up their fleets by giving more street space to buses. But in New York, the voices of drivers and business leaders are often louder than those of the city’s 1.2 million daily bus riders, many of them working-class New Yorkers.

A spokesman for the mayor, Charles Kretchmer Lutvak, said in a statement that the Adams administration had improved commute time on many bus routes, including on Northern Boulevard in Queens, and “continues to do everything we can to meet the ambitious goals that the mayor laid out in his campaign.”

But as Mr. Adams, a Democrat, gears up to run for re-election in 2025, his administration has been deferential toward powerful interests and local leaders.

One of the mayor’s closest aides, Ingrid Lewis-Martin, has opposed street redesign projects and overrode the transportation commissioner in February 2022 to allow cars back onto an eight-block stretch in Fort Greene, Brooklyn, reserved for pedestrians.

Ms. Lewis-Martin also raised concerns about two bike lane plans in Brooklyn: one on McGuinness Boulevard in Greenpoint opposed by Gina and Tony Argento, influential Democratic donors to Mr. Adams who own a local film production company; and another on Ashland Place in Fort Greene opposed by Two Trees Management, a major real estate firm led by an Adams donor, according to two people who were familiar with the matter.

Mr. Lutvak denied that Ms. Lewis-Martin had meddled in the Ashland Place project and said that it was moving forward. On Wednesday, he said the city was also proceeding with a scaled-back version of the McGuinness Boulevard project, a development first reported by Gothamist.

Oswald Feliz, a local City Council member who is part of Mr. Espaillat’s so-called Squadriano political alliance, is fighting the proposal for Fordham Road, which has 85,000 daily bus riders. He, along with other opponents like the Bronx Zoo and Fordham University, fear that the plan would snarl car traffic and push it to surrounding streets because cars would be confined to one lane in each direction. Less than 6 percent of visitors who drive to the zoo and other nearby attractions use Fordham Road to access it, Department of Transportation data shows.

Mr. Feliz would rather have the city repaint the existing bus lanes red and install more traffic enforcement cameras.

“We would strongly support a busway or offset bus lanes in neighborhoods where they are necessary for faster buses; but what Fordham buses need is a fixing of current bus lanes,” he said in a statement.

Mr. Espaillat discussed the Fordham Road plan in a phone call last month with officials from the M.T.A., the governor’s office and the city’s Transportation Department and told them it was clear it did not have local support, according to a person who was on the call and granted anonymity to discuss a sensitive matter. The call was first reported by the website Streetsblog.

A spokeswoman for Mr. Espaillat, who is Dominican American and a key ally in Mr. Adams’s coalition of Black and Latino leaders, said in a statement that he backed local officials “to make the best determination in the interests of city residents.” She noted Mr. Espaillat’s past support for faster bus routes when he was a state lawmaker.

Mr. Davey, noting that the city Transportation Department was short-staffed, said he was so eager to help the city start construction on the Fordham Road project this year that “I’ll go out and paint, personally, a bus lane.”

Opponents of the Fordham Road plan include a business group led by Peter Madonia, a bakery owner and former chief of staff to Mayor Michael R. Bloomberg, and donors to Mr. Adams such as John Calvelli, executive vice president of the Bronx Zoo, and Marc Jerome, president of Monroe College.

The corridor was originally expected to become a busway, like the one on 14th Street in Manhattan that bars almost all through traffic except for buses and commercial trucks and has been shown to improve service. After a stretch of Main Street in Flushing, Queens, was turned into a busway in 2021, rush-hour bus speeds rose by 50 percent. A new compromise proposal would add an “offset lane” for buses in the middle of Fordham Road, allowing for a parking and loading lane next to the curb.

A letter to the mayor from Mr. Feliz and three state lawmakers last month said the new plan would “negatively impact our thriving economic, social, and health ecosystem,” which includes Little Italy on Arthur Avenue in the Bronx and “destinations for visitors and others to the Bronx from all over the world.”

Transit advocates have pushed back, sometimes in eye-catching ways: A giraffe costume was deployed to draw attention to the Bronx Zoo’s opposition.

“Riders are demanding that the mayor keep his promise, and nowhere is that promise more significant — more meaningful — than on Fordham Road,” said Danny Pearlstein, a spokesman for Riders Alliance, a transit advocacy group.

On a scorching hot day last week, Jennifer Reyes, 18, waited for the Bx12 bus on Fordham Road, which she takes to school, Marine training and a job as a cashier at a fried chicken restaurant in Times Square. Ms. Reyes, a lifelong Bronx resident, said buses often arrive late and are too packed to board, so she leaves home early to make up for frequent delays.

“I know it’s going to, like, make people mad,” Ms. Reyes said of the proposal to prioritize buses. “But us students, workers, we need to get to our places.”

Milagros Matías, a home care worker, said she was frustrated by the number of delivery vehicles clogging the street and hoped the city would move quickly to clear the way for buses.

“There needs to be more space for public transit,” Ms. Matías, 54, said in Spanish. “This mode of transportation is essential.”

Jeffery C. Mays contributed reporting.