It was mainly supporters who showed up to clap and chant, “Pay that toll! Pay that toll!” But one opponent tried to drown them out by banging a cowbell. And the exchanges grew a bit testy at times across the congestion pricing divide.

The tolling program, the first of its kind in the nation, finally became reality on New York streets after decades of battles over efforts to unclog some of the most traffic-saturated streets in the world. In the weeks leading up to its start, the program survived multiple legal challenges seeking to derail it at the last minute, including from the State of New Jersey.

It will most likely be some time, however, before it becomes clear whether congestion pricing works, or whether it can withstand continuing attempts to overturn it by a broad array of opponents, including President-elect Donald J. Trump, who takes office later this month.

Noel Hidalgo, 45, who lives in Brooklyn, was among the first drivers to pay the toll. As he drove his Mini Cooper across the threshold, toll supporters cheered and clapped from the curb.

Another driver posted a photo on social media of a silver car with metal cans dangling from the rear bumper. “Just tolled” was written on the rear windshield.

Most passenger cars are now being charged $9 once a day at detection points set up along the borders of the new tolling zone, from 60th Street to the southern tip of Manhattan.

Shortly after noon, about 12 hours after tolling began, transportation leaders declared that the plan had rolled out without a hitch, but cautioned that the tolling system was complicated and that it was too soon to know how it was faring.

“We will start to know specific numbers and have some comparatives within a few days, and we’re going to share that information publicly,” said Janno Lieber, the chief executive of the Metropolitan Transportation Authority, the state agency overseeing the program.

So far, the M.T.A. does not intend to make any adjustments to the program, Mr. Lieber said.

Traffic data for the congestion zone was mixed on Day 1. The average travel speed initially inched upward 3 percent to 15.1 miles per hour at 8 a.m. Sunday, compared with 14.6 m.p.h. at the same time on the first Sunday in January last year, according to INRIX, a transportation analytics firm. But by noon, the travel speed had fallen to 13 m.p.h., slightly slower than in 2024.

Still, the real test for the tolling program will come during the workweek. The M.T.A. said it had chosen to introduce the program on a Sunday to be able to work out any kinks while traffic was sparse. Light snow was forecast for the region on Monday, which could affect commuter data if fewer people choose to drive.

On a typical weekday, at least half a million vehicles enter the congestion pricing zone, a metric that officials will be tracking “very, very closely,” Mr. Lieber said.

Manoj Bhandari’s car will no longer be among them. Though he normally drives into his Midtown office at least twice a week from New Jersey, he said he would now only take the train. “It’s expensive for me and it’s expensive for everybody,” said Mr. Bhandari, 54, who was parked outside the Lincoln Tunnel on Sunday. “We won’t be using our car anymore.”

Transportation officials have projected that congestion pricing will reduce the number of vehicles entering the congestion zone by at least 13 percent.

Other drivers seemed to accept that there was no way around the new tolls. Oscar Velasquez, 54, a carpenter who lives on Long Island, said he was going to have to pay more now to haul his tools to jobs around the city. “One of these days, they’re going to charge you for walking,” Mr. Velasquez said as he idled on West 66th Street in his Chevy pickup truck.

The tolls are expected to help generate $15 billion to pay for crucial repairs and improvements to New York’s aging subway system, buses and two commuter rail lines. The work includes modernizing subway signals, making stations more accessible for riders with disabilities and expanding the city’s electric bus fleet.

Those upgrades could improve the commute for Emily Rose Prats, 36, of Brooklyn, who supports congestion pricing. She has spinal degradation and standing for long periods can cause her great discomfort, so she has avoided the subway and the bus, which can be unreliable.

“The improvements from congestion pricing are supposed to be an upgrade to the signals, which will mean faster trains, shorter headways, shorter commutes, less wait times,” Ms. Prats said. “All of that is something that will help me be able to take advantage of a public amenity that we pay for.”

Congestion pricing is being introduced in New York at a time when traffic has surged on city streets since nearly disappearing five years ago in 2020 at the height of the coronavirus pandemic. New York was named the world’s most congested city, beating out London, Paris and Mexico City, in a 2023 traffic scorecard compiled by INRIX.

Though congestion policy has successfully reduced traffic in other global cities, including London, Stockholm and Singapore, it has never gotten far in this country. Besides New York, a handful of other cities, like Washington and San Francisco, have explored the concept.

The program has been unpopular in the polls, and some transit experts noted that neither Mayor Eric Adams nor Gov. Kathy Hochul had commented on the start of congestion pricing by Sunday afternoon even though it will have a major impact on the city and state.

Mr. Adams has supported the plan while expressing reservations about it, and is running for re-election this year. Ms. Hochul paused the program in June over concerns that it would hurt the city’s recovery and brought it back in November with a 40 percent reduction in the tolls, down to $9 from $15.

The tolls will increase to $12 by 2028, and to $15 by 2031. The new plan is set to generate about $500 million per year during its first three years, and then $700 million when fees first go up, then close to $1 billion when the original toll is restored. The money will be used to secure $15 billion through bond financing, which would be paid back with tolling revenue.

Mr. Lieber of the M.T.A. said that officials did not expect New Yorkers to change their behavior overnight.

“Everybody’s going to have to adjust to this as more and more people become aware of it and start to factor it into their planning,” he said.

At a coffee shop near Lincoln Center, Terry Kotnour, a retired consultant, praised congestion pricing. “That’s the cost of living here,” said Mr. Kotnour, 82, who gave up his car long ago. “We have fairly good mass transit, so use it instead.”

Another supporter, Kevin Chau, 27, a software engineer from Queens who rides Citi Bike, said that he hoped Manhattan would become safer for cyclists. “Less cars on the road means it’s less dangerous for sure,” he said.

But many critics, including suburban commuters, said the program will do little to reduce traffic while punishing drivers who live outside Manhattan.

On the same day that congestion pricing began, the Port Authority of New York and New Jersey also began to charge drivers higher fees to travel between New Jersey and New York on bridges and tunnels, which it controls. (The rate is now $16.06 for passenger vehicles during peak hours, up by 68 cents from the previous fee.)

Roselyn Cano, 21, just bought a car last week to commute from the Bronx to her job at an exercise studio on East 59th Street in Manhattan because she did not feel safe taking the subway. “And then a couple of days later we get hit with the congestion toll,” said Ms. Cano, who sat at a reception desk at the studio tallying up the costs of the new toll along with her car payment, auto insurance, parking and the toll she already pays crossing from the Bronx into Manhattan.

Some New Yorkers were already devising workarounds to avoid paying the new tolls.

Cynthia Jones, who lives on the Upper West Side, was taking an exercise class at the studio. Her husband had dropped her off at 61st Street, one block north of the tolling zone. “I walked the rest of the way here,” she said.

Reporting was contributed by Wesley Parnell, Bernard Mokam, Nate Schweber, Olivia Bensimon, Anusha Bayya, Camille Baker, Sean Piccoli and Emma Fitzsimmons.