New York's Penn Station grinds to a halt the day before Thanksgiving: Night of travel chaos as 43 million Americans try to make it home

Fog clogging Chicago, rain lashing the northeast and a planned labour march at Los Angeles Airport on Wednesday are likely to bring delays, lines and fustrations on the busiest travel day of the year. Motorists can also expect to be travelling bumper-to-bumper by around 5pm, the AAA warned, as more than 39 million people take to the nation's roads, travelling at least 50 miles each.

• Penn Station shuts down all train traffic due to a switching problem with the tracks 
  
• A record 43 million people travelling during Thanksgiving
• Ninety per cent will travel by road - and gridlock is expected by 5pm
• Dense fog cancels and delays hundreds of flights from Chicago
• Workers' union march at LAX expected to cause more chaos

Hundreds of travelers are trapped at New York City's Penn Station on the eve of Thanksgiving as all train service has been suspended to and from on of the city's busiest transportation arteries.

Train service was indefinitely suspended at 5:20 p.m. due to a switching problem in the tracks right at the point where trains enter and leave the station, transportation officials said. The suspensions include all three train services: Amtrak, New Jersey Transit and Long Island Rail Road.

The switching kink has led to severe overcrowding in New York City's biggest train hub on one of the busiest travel days of the year, as hundreds upon hundreds of travelers were scheduled to head home tonight for the Thanksgiving holiday. 

Trapped: Hundreds of travelers are trapped at New York City's Penn Station on the eve of Thanksgiving as all train service has been suspended to and from on of the city's busiest transportation arteries

Locked out: Police prohibited travelers from entering Penn Station until service was restored

Disruption: Train service was indefinitely suspended at 5:20 p.m. due to a switching problem in the tracks

Police have prohibited travelers from entering Penn Station until service is restored to try and mitigate the crowding. Authorities are not forcing anyone out of the building.

With Penn Station closed, some travelers may opt to drive to their destinations. But with the roads clogged with congestion, they may not find that driving gets them to their destinations any faster. More than 39 million people were expected to take to the nation's roads around 5 p.m. Wednesday, driving at least 50 miles each, according to AAA.

There will be similar struggles for travelers taking to the air, as already 300 cancellations and more than 4,200 delayed flights have been reported as the north suffers poor weather.

Chicago O'Hare and Midway airports have been hard hit by dense fog, with as many as 180 flights cancelled and 680 delayed, causing slow-moving lines to snake through terminals.

Shut down: Among the services suspended at Penn Station Wednesday was the Long Island Rail Road, which serves nearly 300,000 passengers on a typical day

Let the chaos begin: Travelers wait in a long line to pass through security at Reagan National Airport in Arlington, Virginia as more than 43 million people are predicted to travel during Thanksgiving

Warnings: A sign alerts travelers to expect traffic delays at George Bush Intercontinental Airport in Houston

Heading home: People wait to board a Bolt bus outside Penn Station in New York on Wednesday

O'Hare is the second biggest airport in the U.S. and a major hub for both United and American airlines while Midway is one of the biggest bases for low-cost giant Southwest.

The cancellations are likely to spark problems for thousands of travellers in other areas of the country where the weather is fair.

The city’s aviation department predicted that nearly 1.8 million travellers will use the two airports over the eight-day Thanksgiving travel period, which ends next Tuesday.

'Both are reporting visibility near zero,' Gino Izzi, a meteorologist at the National Weather Service, told the Chicago Tribune of the airports. 'It’s going to be an absolutely awful morning, and will probably go into the afternoon at most airports.'

Disaster: Fog descends upon Chicago's O'Hare International Airport as holiday travel begins on Wednesday

Fog: Travelers posted pictures to social network sites of the fog clogging Chicago on Wednesday

Struggle: Visibility was also poor on roads in Illinois, Missouri, Wisconsin, Iowa and Indiana

Dense: The fog in Chicago, pictured, will also impact other flights in areas of the country where weather is fair

Travellers nervously watched departure boards inside the airports, hopeful that the fog would pass and clear the delays, which are 90 minutes on average.

'We couldn't see any road signs in front of us, or the house next door, so we left three hours early,' Hannah Ducey, who is travelling to Nashville, told CBS at O'Hare.

Lines also stretched along expressways in Illinois as drivers battled with the fog. Around two million people will take to the roads across the state, a spokesperson from the AAA said.

'I think the fog is going to have some effect on either people's decisions on when they’re going to leave or certainly, if they're out, in getting to where they want to go today,' she added.

Busy: More than 39 million Americans are expected to drive during the upcoming Thanksgiving holiday

Full: Passengers wait in line to pass through security at O'Hare Airport on Wednesday as flights are delayed

Trying: Travellers wait at the Amtrak station in downtown Milwaukee to travel to Chicago on Wednesday

Long wait: People line up at LaGuardia airport in New York as Thanksgiving travel begins

Plans: Travelers check their flights at Chicago's O'Hare Airport, where hundreds of flights are delayed

A dense fog advisory is also in effect for much of Missouri and Wisconsin, as well as eastern Iowa and northwest Indiana.

But the weather could also spell trouble for motorists in the Pacific Northwest, where travellers should be braced for a soggy ride.

Oregon has experienced up to 10 inches of rain, and there have been nine inches in some parts of Washington and 6.5 inches in Northern California.

And while weather should remain mild for motorists along the East Coast, families should still expect slow-crawling traffic across the entire country.

Roads in New York, Washington D.C, Chicago, San Francisco, and Los Angeles will be particularly trying, with journeys expected to take 33 per cent longer than usual, ABC reported.

The AAA suggests families travelling on the country's roads leave as early as possible, and should expect to be travelling in gridlock by around 5pm on Wednesday.

'With today expected to be the busiest day, and many people also working, we're expecting this evening there will be a lot of congestion,' AAA spokeswoman Heather Hunter said.

Trouble: A map of the U.S. shows the stretch of heavy fog in the north on Wednesday morning

Soaked: Another map shows how motorists in the northwest can expect a soggy journey on Wednesday

Patience: Marissa Zendzan, 7, of Raleigh, North Carolina, waits for an Amtrak train with her father

Heading off: Fred Errington and Deborah Gewertz wait for a train to arrive at Union Station in Hartford, CT

Families travelling through Los Angeles can also expect delays as airport union workers prepare to strike on Wednesday morning in a battle over health insurance plans.

The march, comprised of more than 1,000 workers and their supporters, could snarl traffic around the airport on the already-hectic travel day, Los Angeles International Airport officials said.

The airport warned travellers to add 90 minutes to their planned arrival times.

Even the workers admit they could not have picked a worse day or a busier airport, ABC reported.

'It's a national day about being with your family and taking care of your family, and these workers are not able to do that,' Andrew Gross Gaitan, from the Seiu United Service Workers West, said.

Queues: A woman pulls her suitcase as passengers wait to board a train in New York's Penn Station

Swamped: Passengers wait in line to board their trains at Union Station in Washington, DC on Wednesday

Long journey: People wait to board trains at Penn Station in New York during the year's busiest travel day

Crowded: A woman sits on the floor as people wait to board trains at Penn Station in New York

The number of travellers flying is down this year, to 3.1 million, even though the average domestic airfare is down 11 per cent compared to last year.

But travel company Orbitz said most planes will still be full throughout Thanksgiving.

'We're not expecting a big drop in the number of people on planes. People still want to get away this weekend,' said Jeanenne Tornatore from the company.

Thanksgiving is also the busiest time of the year for Amtrak, which has borrowed carriages from its Canadian counterpart to make 300 additional seats available on trains running in the Northeast.