NEW YORK (AP) — Airports in New York, Boston and Connecticut were ramping up service Sunday, as they worked to return to normal operations following a massive snowstorm that crippled parts of the East Coast and led to thousands of flight delays and cancelations.

Airlines said they were operating close-to-normal schedules on Sunday, a busy day for air travel.

Meanwhile, trains and public transportation networks were also struggling to get back to full operation in time for Monday morning's commute.

Boston's Logan Airport opened at 11 p.m. ET on Saturday, after closing in anticipation of the storm along with airports in New York City and Connecticut.

As of Sunday afternoon, Boston was still experiencing delayed and canceled flights and officials urged passengers to check with their airline before heading to the airport. Connecticut's Bradley International Airport opened early Sunday morning, also advising passengers to contact individual airlines about possible cancellations.

Flight-tracking website FlightAware.com said about 450 flights were canceled on Sunday, a busy travel day for airlines. Only 20 are expected for Monday.

In all roughly 5,700 flights have been canceled since Friday, when the airports shut down in anticipation of the storm. Friday saw the most cancelations, according to FlightAware, with Saturday a close second. Airlines waived ticket-change fees for passengers in the affected areas.

Airlines try to get ahead of big storms by canceling flights in advance. They want to avoid having crews and planes stuck in one area of the country. They also face fines for leaving passengers stuck on a plane for more than three hours, under a rule that went into effect in 2010.

Delta Air Lines Inc. said that as of Sunday morning, its flights were back to normal. In all, it canceled about 1,200 flights due to the storm.

United Airlines spokeswoman Megan McCarthy said the airline was operating at all airports Sunday, though it was experiencing some delays because of the weather. United is part of United Continental Holdings Inc.

American Airlines spokesman Kent Powell said that by Sunday afternoon the storm-related cancellations had become "almost a non-issue."

JetBlue Airways Corp. said flights are back to regular schedules in New York and will be in Boston by Monday.

Amtrak trains were running on a limited schedule between New York and Boston, after service between the two cities was canceled Saturday.

Regional lines were still working to restore service.

As of Sunday afternoon, Metro-North Railroad service on the New Haven Line was operating between New York City and Stamford, Conn., but remained suspended between Stamford and New Haven, and on branch lines. Train crews were working to clear as much as 4 feet of snow off the tracks.

The Long Island Rail Road was back to "near-normal" weekend schedule on the western portion of most of its lines, New York's Metropolitan Transportation Authority said. But train service in Long Island's Suffolk County, also hit with more than two feet of snow, was suspended.

Most New York City subways and buses were operating on a regular schedule.

The Massachusetts Bay Transportation Authority said service on some subway and bus lines resumed at about 2 p.m., and planned to operate on regular schedules Monday. But the agency said commuters should expect "significant" delays.

Most commuter rail service around Boston should resume by Monday morning, the agency said on its website.

The blizzard also snarled drivers across the Northeast as snow cleanup continued Sunday.