Plus, I have seen many idiots with newer cars that have the light switch set to "auto" during fog. The car sees there's enough light, even in fog, and keeps on the DRL's. When the DRL's are on, there isn't a single light that's turned on in the back. And that's pretty much a recipe for disaster, especially if you're driving slow.
Dimmed headlights, fog lights and four-way blinkers in thick fog. As well as mandatory speed reduction.
On highways in my country, there are these dots painted in the emergency lane:
And these signs posted:
Even without translating I think you guys can get what these signs are trying to tell you!
