With Thanksgiving on the horizon, the holiday travel rush is already underway at Long Island MacArthur Airport, where passengers streamed through the terminal Tuesday in anticipation of family gatherings, crowded tables — and crowded skies.

Travelers crisscrossed the concourse with rolling suitcases, kicking off what is expected to be one of the busiest travel periods since before the pandemic. Millions of Americans are flying this week, prompting U.S. Transportation Secretary Sean Duffy to call for patience — and polish.

Airlines have reported a 400% increase in passenger outbursts since 2019, with the bulk of those incidents happening in 2021. Duffy says a little effort in appearance might go a long way toward better behavior.

“I would encourage us to dress a little better, which encourages us to behave a little better,” Duffy said. “Let’s try not to wear slippers and pajamas as we come to the airport.”

Some travelers at MacArthur appeared to take the advice to heart. Passenger Max Bartee said he made an effort, sporting Vuori dress pants — though he paired them with Skechers slip-ons and a T-shirt featuring his favorite East End hangout, Cooper’s Beach.

“I was dressing up just a little bit more than normal,” Bartee said.

While airport traffic surges, the roads are also expected to be jammed. That’s enough to keep some Long Islanders home for the holiday. George Trent, of Shirley, said he has no intention of battling the bumper-to-bumper crowds.

“Holiday time is horrible — everyone comes from out of state and floods the roadways,” he said. “Stay home with the family, enjoy the kids and enjoy the holiday.”

For others, the spirit of the season is a reminder to stay patient amid the rush.

“It’s a season of thanks, and people should be civil and kind to each other,” said Johanna Miller, of Smithtown.

Travelers flying this week are being urged to arrive early to allow extra time for check-in and security.