I counted quite a few folks who didn't have their headlights on Monday afternoon on my way into work. When your windshield wipers are going your headlights have to be on. It's the law. But when it's foggy your headlights should be on as well. This is so other drivers can see you from the front AND back. The tail lights do not turn on when just your daytime running lamps are on, so traffic coming up from behind may not be able to easily see you.
With the potential for dense fog Tuesday morning, it's important that everyone remembers to turn their headlights on.