Taxis, but Not as Many as Usual, Are Among Only Transit Options During Storm The taxis gathered outside of the Port Authority Bus Terminal, as if out of habit, waiting for passengers whose rides to New York had never materialized. Wayfarers slogged up a ghostly Broadway, its lights dimmed beneath the graying sky, or squinted through full-body ponchos as they churned their bicycles to get to work. And a curious few breached the barricades outside of New York City's subway stations, sneaking a peek at the system that never sleeps, sleeping. This was the view from the nation's most sprawling transportation hub, surrendering its advantages bit by bit. The subways were gone, probably until at least Wednesday, officials said. Buses and commuter rail systems were suspended. Amtrak and many major airlines canceled trips throughout the Northeast for Monday and Tuesday. By midmorning, much of the Franklin D. Roosevelt Drive was underwater, shuttering 63 blocks" worth of northbound lanes. By the afternoon, the Holland and Brooklyn-Battery Tunnels were closed, too. And by nightfall, Hurricane Sandy had nearly isolated the island of Manhattan: the East River crossings like the Brooklyn and Manhattan Bridges, were closed at 7 p.m., as were the George Washington, Verrazano-Narrows, Whitestone and Throgs Neck Bridges, among others. Even with the Lincoln and Queens-Midtown Tunnels remaining open Monday night, it was clearly the transportation system's most helpless day. At first, New Yorkers improvised. There were fewer yellow taxis than usual - roughly 4,000 at noon, the city's taxi commissioner, David S. Yassky said, about a third of what is typical - but with many schools and businesses closed, there was also little competition. "People may be afraid," Tariq Minhas, 54, said of his fellow yellow-taxi drivers on Monday morning. Some probably stayed home because they required mass transit to get to their depots each morning. But Mr. Minhas, of Bensonhurst, Brooklyn, said he saw the transit shutdown as a business opportunity. He approached the taxi line at the Port Authority Bus Terminal around 8 a.m., but decided to head east, where he could more actively hunt for his next fare. For-hire vehicle operators, like Carmel Car and Limousine Service and Dial 7, said they were booked throughout the day on Monday. Dial 7 said on its Twitter page that no new reservations would be accepted until 10 a.m. on Wednesday. "This is not a time to make money," said Avik Kabessa, Carmel's chief executive, who noted that business was down about 75 percent on Monday. We told the drivers to help as much as they can until they feel that driving is no longer safe. Others went to work on foot. Felix Toro, 23, walked from his home in Fort Greene, Brooklyn, over the Manhattan Bridge to his job as a barista at Bowery Coffee on Houston Street. "I didn't want to spend today at home," said Mr. Toro, whose boss offered him the day off. He brought a change of clothes in case he became stranded at the coffee shop. "I don't have a death wish or anything," he said. By late afternoon, this appeared to be the prevailing sentiment across the city. Some of the Manhattan's busiest streets were all but bare, and many yellow-taxi drivers began returning their vehicles to the depot, citing a disappearing customer base. Of course, their mobility would have been limited even if they stayed behind, with the closing of the Holland and Brooklyn-Battery Tunnels at 2 p.m. "We're both in very low-lying areas," Anthony Carvagno, the general manager of the Holland Tunnel, said of the two tunnels that closed. And this is unprecedented. Well before the brunt of the storm was expected to hit, officials observed that water levels were on the verge of overwhelming the pumps. "There's no place for the water to go," said Judie Glave, a spokesman for the Metropolitan Transportation Authority, which operates the Brooklyn-Battery Tunnel. We're pumping water into the river, and it's coming back. For Tropical Storm Irene, the New Jersey-bound side of the Holland Tunnel was closed for only about an hour, Mr. Carvagno said. Other than that time, he did not remember a weather-related closing of the tunnel over his more than 30 years with the agency. The Brooklyn-Battery Tunnel last closed after the Sept. 11 terror attacks. Mr. Carvagno said he expected the tunnel to reopen shortly after the storm, provided power was not lost to the pumps. The same might not be said about the subway system. Joseph J. Lhota, the chairman of the transportation authority, warned at a news briefing on Monday that the expected storm surge posed a significant threat to subway switches and the electronic signaling system. "The general ability to run the system and keep it safe is in jeopardy," Mr. Lhota said. There may be little precedent for such a cleanup at the authority, if the most dire predictions hold. In December 1992, a storm filled three tunnels with water and briefly suspended every subway line. Some lines were restored the same day; the L train under the East River was out of service for several days. This time, the transportation authority said that if subway tunnels that cross beneath the Hudson and Harlem Rivers were to become flooded, pumping the water out could take anywhere from 14 hours to more than four days. If that were to happen, the authority would have to restore signals and other equipment that might have been damaged. Until then, Mr. Minhas, the yellow-taxi driver, said he would continue to work, staking his ground as one of the only remaining transit options in a city typically overrun with them. "I heard on the news," he said of the storm, as he zipped through a light drizzle Monday morning, "it's not yet over."