The National Weather Service issued a dense for advisory for the region Tuesday morning.
The advisory is in effect until 9 a.m. in Lake, Porter, Newton, Jasper, Benton, Cook and Will counties.
Visibility is expected to be reduced to less than a quarter of a mile at times. Forecasters encouraged motorists to leave extra time for travel, turn on headlights and increase following distance.
Area police reported no serious traffic problems related to the fog Tuesday morning.