Published: Jan 11, 2011 5:29 PM EST
Updated: Jan 11, 2011 2:29 PM EST

MIAMI (AP) - Foggy conditions are making driving difficult for some motorists across South Florida.

Authorities closed U.S. 27 from South Bay in Palm Beach County to Interstate 75 in Broward County around 2:30 a.m. Tuesday because of heavy fog. It was unclear how long the road would be closed.

The National Weather Service issued a dense fog advisory until 9 a.m. Tuesday. In some areas, visibility is reduced to a quarter mile or less.

Drivers are urged to slow down and use low-beam headlights.