Those traveling to and from the Philadelphia area for the holidays Wednesday face a foggy, slow start to their journeys.

A National Weather Service dense fog advisory is in place through mid-morning for much of the area.

Motorists should be prepared for poor visibility on the roads. Visibility may be a quarter-mile or less in some places, the weather service said.

The fog and clouds were also leading to delays at Philadelphia International Airport, where delays for arriving flights were averaging more than an hour Wednesday morning.

Delays for departing flights were also reported.

AAA says about 11.1 million people in the Philadelphia area will travel between Wednesday and Jan. 3, a 2.1-percent increase from last year. Most people make their trips by car, according to AAA.