AAA forecasts 79.9 million people will travel by car, plane or another mode of transportation for Thanksgiving -- up 1.7 million people compared to last year.

       Here’s what you need to know before you head to the airport or hit the highway:

       Hopper expects this will be the busiest Thanksgiving holiday ever for U.S. airports, with 36.5 million seats booked between Saturday, Nov. 23, and Tuesday, Dec. 3 -- a 4.8% increase from the same period last year.

       The Sunday after Thanksgiving -- Dec. 1 -- will be the busiest day to fly, according to Hopper.

       The cheapest days to leave for your trip are Thanksgiving Day or three days earlier, on Monday, Nov. 25, Expedia said. The cheapest days to fly home are Black Friday (Friday, Nov. 29) or Travel Tuesday (Tuesday, Dec. 3).

       Expedia predicts the busiest and most expensive days to fly will be the day before Thanksgiving and the Sunday after Thanksgiving.

       The most popular U.S. destinations this year are Atlanta, Los Angeles, Dallas, Las Vegas and Chicago, Hopper found.

       Hartsfield-Jackson Atlanta International Airport, Dallas Fort Worth International Airport and Denver International Airport are poised to be the most crowded airports, Hopper said.

       A record 71.7 million people are expected to travel by car for Thanksgiving -- up by 1.3 million people from last year, according to AAA.

       The worst times to drive before Thanksgiving are the afternoons of Monday, Nov. 25, Tuesday, Nov. 26, and Wednesday, Nov. 27, according to analytics company INRIX. It's best to wait until Thanksgiving Day -- Nov. 28 -- when the roads will be quieter.

       If you're heading home on Saturday, Nov. 30, or Sunday, Dec. 1, INRIX recommends hitting the road before 1 p.m.

       Traffic could be more than double what it is on a typical day in cities including Boston, New York City, Washington, D.C., Los Angeles and Seattle, INRIX warned.

       ABC News' Ayesha Ali contributed to this report.