▶ Watch Video: Flight cancellations prompt fears of holiday travel chaos

The holiday rush is underway — with nearly 48 million Americans hitting the roads or heading to airports for the Fourth of July weekend. Cancellations are stacking up once again though, as U.S. airlines struggle to serve their own customers.

TSA reports that more than 2 million people have passed through airport checkpoints on most days this month as flight traffic approaches pre-pandemic levels. But airlines are struggling to keep up. Since Memorial Day, airlines have canceled more than 21,000 flights — double of last year’s rate.

In an effort to make up for some of those issues, Envoy and Piedmont, two of American Airlines’ regional carriers are offering pilots up to three times the pay to pick up extra shifts. Earlier this year, United and Delta announced schedule reductions for July. Now, some Delta pilots are picketing.

“The problem is they’re trying to operate by responding to demand but they can’t respond to demand that they don’t have the staff to support it,” CBS News senior travel adviser Peter Greenberg said.

Delta is also taking the unusual step of waiving all change fees through Monday, saying it expects “operational challenges” over the weekend.

Travelers who choose to drive instead of fly will face high prices at the pump. The national average is down since climbing above $5 per gallon two weeks ago, but remains high at $4.86 — $1.75 more than a year ago.

Farokh Karani told CBS News transportation correspondent Errol Barnett that the potential airport chaos is just too much.

“The planes are packed. You have delays, God help you if you have a delay,” they said. “I’m now a committed driver, at least until things improve, you know, being able to make flying convenient again.”

Transportation Secretary Pete Buttigieg told CBS News that his agency is engaging with the airlines every day on being more reliable. Today, the airlines and FAA held a meeting to discuss their “shared commitment to minimizing disruptions and providing a safe, efficient journey for all travelers.”