SAN FRANCISCO INTERNATIONAL AIRPORT (KGO) -- AAA says today is the worst day to travel across the nation for the holiday season.
They predict more Americans will travel by car this holiday season than ever before.
Airports are also packed. The 6.7 million people traveling by plane this year is the highest level in 15 years.
RELATED: Can you take wrapped presents on a plane? Holiday travel tips from TSA
San Francisco International Airport says today and tomorrow will be the busiest days for the Christmas holiday.
The Howe family braved long lines inside SFO as they head to Kansas City.
"I'm very excited, said Lily Howe, "cause it's snowing."
The dense fog was a problem for passengers coming in and out of SFO. Delays averaged 45 minutes mid-morning. Several flights were canceled.
VIDEO: Bay Area AccuWeather forecast
SFO recommends you sign up for notifications from your airline in case your flight is delayed or canceled.
Check drive times and traffic maps before heading out the door.
Today is busiest day for holiday travel, according to AAA