Driving slowly in the fog is just for driving newbs and the super-cautious, right? Nope. Although you may know the roads you drive like the back of your hand, you literally can't see the road in front of you when it's really foggy. Besides not driving at all, slowing down is one of your best options for avoiding an accident in these conditions.
Even if you don't think you're driving fast in the fog, check your speedometer. Fog can actually cause a visual illusion and make it look like you're moving slower than you actually are. Without reference points like buildings, trees or other objects, you'll have a hard time gauging just how fast you're going without taking a good look at that Speedo. Or, uh...speedometer. We meant speedometer.
If you do hit an unexpected patch of fog, don't slam on the brakes. Ease off the accelerator and then use the brakes only if you need to. Hitting your brakes hard will be an unexpected move to the cars behind you, and you may even cause them to slam on their brakes as well. This is how a lot of chain reaction pile-ups are caused on the roads.