“The subway and our unparalleled 24-hour-a-day mass transit network are the engines that power a city economy that continues to grow and outpace the nation,” said John J. McCarthy, a spokesman for the Metropolitan Transportation Authority, which operates the subway. “Chairman Lhota’s subway action plan is stabilizing the subway by targeting the biggest drivers of delays across the system.”

Those problems include outdated switches, overcrowding, sick passengers and trains with mechanical difficulties, the report found.

“There will be events such as power outages and derailments that cause more severe systemwide delays, as well as days on which the system runs very smoothly and the total time lost to delays is less than the average we have estimated,” the agency’s report noted.

But for riders like Major Stevenson, 24, who relies on the E line from its terminus in Jamaica, Queens, to travel into Manhattan, the problems plaguing the system have had a personal cost.

“I’ve lost my job, because of the subways,” Mr. Stevenson, a construction worker, said on Tuesday morning, as he waited for an E train to arrive at the Court Square station in Queens. He got there too late.

When his company had a job near the 42nd Street station in Manhattan, he left his home two hours early, giving himself additional time like many New Yorkers do for all-too-frequent delays. But on that day, Mr. Stevenson and his fellow workers found themselves stuck underground in Queens for more than an hour.

“We lost that contract because of that,” he said. “I had to go somewhere else to find work.”

Mr. Stevenson said that many construction workers he knows rely on the subway to get to locations all over the city. Bad service, he said, is a constant threat to financial stability.