My commute includes 10 miles of a MUP that parallels a river. The last couple of weeks there's been a couple of mile section with fog dense enough (coupled with kamikaze deer) that I had to slow down. I'd estimate visibility was no more than 30 ft. I ride this MUP a lot, and I still got disoriented and almost missed a turn. As others have said, the high powered lamp on my helmet did more harm than good (at least for my ability to see), but I felt OK with my Dinotte 300 on steady and a Niterider 2W Solas flashing behind me.