PHILADELPHIA (WPVI) -- Triple A estimates that 3.7 million people will fly through Sunday to get where they need to go for the holidays.
On Monday, the State Department issued a warning to all United States travelers.
"Fortunately it's the world we live in," said one traveler.
Flyers have mixed feelings about the warning from the State Department telling Americans to be alert to possible travel risks over the holidays.
"I think it's worrisome to all people what happens in regard to Paris, yeah, so I'm a little worried," said Marisol Velez.
Another traveler said, "You can't let it hold you back, you know what I mean. You got to keep on going with it. I'm not going to let it stop me," said Jeremy Valenzuela.
Michael Tiffany added, "It's not going to deter me from travel, but it doesn't necessarily make me feel safer."
The alert comes on the heels of threats made by ISIS to New York and Washington, D.C.
At Philadelphia International Airport expect to see K-9 units now out in the open. Previously they were behind the scenes. That measure was planned before Monday's alert.
Security is expected to be tighter across the country, especially with the recent attacks in Paris, and heightened measures in Belgium.
Authorities say expect stiffer measures throughout the week.
Even TSA pre-checks may have to take off their shoes or undergo random checks.
TSA would not elaborate on what those extra safety measures are, but they are asking for all flyers to head to the airport a little earlier, so your wait time won't be so long.
Safety measures during the holiday travel
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