One hundred million holiday travelers will hit U.S. roads this week — more than any year ever, experts said.

And AAA New York spokesman Robert Sinclair Jr. said that’s for one reason: “Gas, gas, gas.”

With the national average price of a gallon of unleaded gasoline dropping below $2 for the first time in nearly seven years, Sinclair said Americans who would typically do their reveling around their own Christmas tree will venture out to visit loved ones this week. One in three Americans is expected to journey 50 miles or more from home this week — the busiest travel week of the year, according to the AAA.

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Historically high temperatures — expected to top 70 degrees Wednesday — also make a holiday road trip a little more bearable, Sinclair said.

“Without a doubt it certainly makes travel easier,” said Sinclair, who noted that last year’s holiday travel week came days after a major blizzard. “That would certainly put a damper on going out at all or the distance that you travel.”

Airports will also be especially packed this week. The Port Authority of New York and New Jersey expects 5.4 million people will travel through its airports from Dec. 17 to Jan. 1 — an increase of more than 12 percent over last year.

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“The unusually warm weather this season means passengers don’t have to worry about snow shutting down the airport — but the rain and fog may still slow down flights this week,” said Joe Sitt, chairman of the Global Gateway Alliance, a New York airport travelers’ advocacy group. “Because the Federal Government has not done enough to modernize air traffic control, even mild weather like rain will continue to delay millions of passengers.”

The Long Island Rail Road said it will do its part to help holiday travel. Wednesday, the LIRR will operate 13 additional early getaway trains departing Penn Station between 12:43 p.m. and 3:48 p.m. “to accommodate the large number of customers expected to leave work early to begin their Christmas holiday.”

Photo Credit: James Carbone

The extra trains will run on the Babylon, Far Rockaway, Port Jefferson, Port Washington and Ronkonkoma branches. On Friday, Christmas Day, the LIRR will operate on a holiday schedule.

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Amtrak will also be boosting service as needed this week, spokesman Craig Schulz said, including by adding extra cars to trains and providing more long-distance travel opportunities for riders in the Northeast.

Schulz said Amtrak has also stepped up its security efforts this week, including by activating new crash-prevention technology between Philadelphia and New York. The positive train control system uses radio transponders to automatically slow or stop a train when it violates a signal or exceeds speed limits.

“During the holiday season here, when we have extra guests on the railroad, it’s good to know that we have this added level of security keeping everybody safe,” Schulz said.

Suffolk County Police Chief Stuart Cameron on Tuesday announced the enhanced use of explosive-sniffing dogs at Long Island MacArthur Airport in Ronkonkoma. Canine officer Unser, who is trained to detect explosives from hundreds of yards away and works in the airport regularly alongside handler Officer Michael Canavaciol, will be used more frequently to detect potential threats in the secured areas of the airport, Cameron said. The department’s other bomb-sniffing dogs will be used in a heavier rotation at the Islip Town-run airport.

Officials said that on a normal day, about 1,500 people pass through MacArthur, but during peak holiday travel periods, that number swells to about 2,000 people.

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“We’re trying to adapt,” Cameron said. “We’re always trying to keep ahead of the terrorist groups, to keep the people that travel through MacArthur Airport safe.”