Determined Hudson Valley commuters began their return to work Thursday -- and what promises to be a much longer trek to normalcy after superstorm Sandy -- as the MTA resumed service on two Metro-North Railroad lines as well as some subway service in New York City.

About 356,000 Westchester, Rockland and Hudson Valley customers remained without electricity Thursday morning, 55 percent of them in Westchester.

Westchester County Executive Rob Astorino, in a tweet Thursday, said he was "demanding answers" from the chiefs of Con Edison, which serves most of the county, and NYSEG.

Motorists faced debris-strewn, darkened roads. Lines were long at the few gas stations open and cellphone service was spotty after Sandy knocked out towers.

Commuters from the northern suburbs taking the George Washington Bridge were stuck in bumper-to-bumper traffic as officials decreed that only cars with three or more passengers would be allowed into Manhattan from 6 a.m. until midnight. Metro-North was providing capacity for about 70,000 people -- half its usual ridership -- as service on its other lines remained suspended.

Metro-North will "strive" to reopen the northern segment of the New Haven line Thursday after resuming service from Mount Kisco to Grand Central on Wednesday, a spokeswoman said. The commuter rail line also resumed service on the Harlem line from Mount Kisco to Grand Central Wednesday. At the White Plains station, 20-year-old Shaunice Alexander was resigned to the difficulties as she traveled to work at the New Victory Theater in midtown Manhattan.

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"It's up and running and it's only been, what, a couple of days?" said the White Plains resident. "It was a storm, what are you going to do?" she said of the MTA.

Mayor Michael Bloomberg decreed that every car entering Manhattan had to have at least three passengers. Traffic and confusion reigned at the East River crossings. Some workers found their way to the Ed Koch Queensboro Bridge and walked across.

At 7:03 a.m., a Delta Air Lines plane bound from Syracuse touched down at LaGuardia, the first flight at the airport since Sandy swept onto the East Coast Monday night. LaGuardia, the fifth and final Port Authority airport to reopen, will ramp up service throughout the day, said a spokesman, who urged travelers to confirm their flights with the carrier before heading to the airport.

Gov. Andrew Cuomo announced late Wednesday night that fares for subways and rails would be waived through Friday, to encourage people to use mass transit instead of driving into the city. Previously, fares had been waived for buses.

Two days after Hurricane Sandy's deadly winds stopped blowing, more than 380,000 people in the Hudson Valley remained without power Wednesday -- and some of them could be for weeks.

Storm-battered residents turned to mobile phones as a communications lifeline, but federal officials said 20 percent of cell towers remained out of service along the East Coast. AT&T and T-Mobile announced they were "merging" their networks in battered areas, letting their competitors' cell tower fill in for ones that are disabled. Verizon Wireless reported that 6 percent of its cell towers in Sandy's path were disabled Tuesday.

Utility companies said the impact was twice as great as 2011's devastating Hurricane Irene -- and estimated that bringing power back up would take anywhere from six days to several weeks.

"This is the worst," Orange & Rockland spokesman Mike Donovan said.

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On Thursday morning, Cuomo tweeted that Manhattan customers will have power restored by Saturday, according to Con Edison.

A trio of rock stars from some of the areas worst hit by the storm, Billy Joel of Long Island and Bruce Springsteen and Jon Bon Jovi of New Jersey will headline an NBC telecast to benefit the American Red Cross at 8 p.m. Sting, Jimmy Fallon and Christina Aguilera also will perform.

In New York, Sandy was blamed for at least 30 deaths, including five in the Hudson Valley and 18 in New York City. The estimated damages: $6 billion in lost revenue statewide, and unallied billions more in damage to infrastructure and property.

Despite the continuing infrastructure issues in New York City, organizers said the New York City Marathon would go as scheduled.

Power should be restored "sooner in Westchester" than Long Island, where 90 percent of the residences and businesses were without power, Cuomo said Wednesday, without specifying a timetable.

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U.S. Sen. Charles Schumer, who joined Cuomo and other officials in a flyover survey of damaged areas Wednesday, said a federal dewatering team from Illinois and workers from around the country are headed to New York City to help clear the tunnels.

A spokeswoman for Con Edison said more than 3,000 wires were down and 800 roads closed in Westchester, where more than 194,608 businesses and homes are without power as of Thursday morning. Full power restoration in the county could take a week or more, a spokesman said Thursday.

Cuomo: We will come back stronger

Cuomo joined Westchester County Executive Rob Astorino, Schumer, MTA chairman Joseph Lhota and other government leaders Wednesday flying over New York City, the Hudson Valley and Long Island, surveying some of the areas most devastated by the superstorm.

While damage to the subway system was extensive, authorities said 14 of the city's 23 subway lines would be running by Thursday morning's rush hour.

"As New Yorkers we've gone through dark times before," Cuomo said. "We came back and we came back even stronger."

Police, Cuomo said, would also enforce a strict requirement that cars entering the city have at least two passengers. The temporary requirement will start at 6 a.m. Thursday and remain in effect through midnight.

"After checking out the damage from a helicopter, Astorino said: "This was a devastating, deadly storm for Westchester."

Downed trees posed the most serious problem in the region, he said, not flooding.

As for Metro-North, waterlogged substations that cannot provide third-rail power and washed-out sections of track are posing problems.

Astorino said he was "amazed" at the coastal devastation, including damage to the boardwalk and ice casino at Rye Playland.

Help is on the way

Hurricane Sandy has inflicted "billions" in damage and President Barack Obama has been supportive, Cuomo said. "We expect the federal government to pick up the lion's share" of the cost, he said. The governor also stressed that bolstering infrastructure is crucial because "this is going to happen again" and we have to build stronger, better bridges, tunnels and roads.

The president toured New Jersey Wednesday, but Mayor Michael Bloomberg urged him to skip New York City because officials are overwhelmed with storm recovery.

Under federal rules, the county would be eligible for federal relief aid if Hurricane Sandy caused more than $3.2 million worth of damage, Astorino said.

"The threshold will be met," he said.

State Sen. David Carlucci urged the Federal Emergency Management Agency to declare Rockland County a federal disaster area.

Transit, roads, slowly ramping up

Westchester was among the Hudson Valley's hardest-hit counties.

Most major roads and bridges have reopened, but the Bronx River Parkway remained partially closed Wednesday. Its southbound lanes were opened Wednesday morning and the northbound lanes were expected to be opened later Wednesday, officials said.

The Sound Shore communities took the brunt of Sandy's powerful winds, as in Mamaroneck, where 70 roads were closed and more than 60 percent of the town was without power.

Officials still weren't sure how badly New York City's subways were damaged -- inspectors couldn't access most of the system because its tunnels were still flooded Wednesday. With 14 of the city's 23 subway lines set to restore limited service Thursday, Bloomberg said it will be at least several days before some subway lines begin running again. Westchester's Bee-Line buses are operating Wednesday.

While Sandy wasn't accompanied by the torrential downpours forecast by some weather models, storm surges caused "unprecedented" flooding in train tunnels around New York City, an Amtrak spokesman said.

Region to remain unplugged

In Rockland County, 67,900 customers remained without electricity Thursday morning, O&R reported. The other blackout totals were: Orange, 47,175; Putnam, 27,472; Ulster, 12,574 and Dutchess, 5,780.

With Sarah Armaghan, John Dyer, Nik Bonopartis, Tim O'Connor, Meghan Murphy, Christian Wade, Kari Granville, Thomas Zambito, Karl deVries, Xavier Mascarenas and The Associated Press