Driving in fog — Illinois Permit Test

In fog a driver should turn off the cruise control, increase the following distance, and drive with the headlights on dim or use fog lights.

High beams bounce off the fog and come back at you. Dim lights go under it, which is why the manual names them.

Drive with your headlights set on dim or use fog lights.

A driver should not overdrive their headlights in fog, should stay within the limits of their vision in case a sudden stop is needed, and should pull off and stop where the fog is too dense.

Overdriving the lights means arriving somewhere before you can see it. In fog that distance can be a few car lengths.

Do not overdrive your headlights. Stay within the limits of your vision in case it is necessary to stop suddenly. If the fog is too dense, pull off the roadway and stop.

In fog a driver should use turn signals long before making a turn and brake early when approaching a stop to warn other drivers.

Your brake lights are the only thing the driver behind can see. Using them early gives them the distance the fog took away.

Use turn signals long before making a turn. • Brake early when approaching a stop to warn other drivers.

Which headlights should an Illinois driver use in fog?

Headlights on dim, or fog lights. High beams bounce off the fog and come back at you. Dim lights go under it, which is why the manual names them. Illinois Rules of the Road 2026, p.84: “Drive with your headlights set on dim or use fog lights.”