Never drive so fast that you cannot bring the car to a safe stop in the clear section of road visible in front of you.
This bit of advice resonated when I woke to the news of the Almö bridge disaster in January 1980. A ship crashed into one of the support arches of tall bridge in the early hours of the morning, and a section of the bridge collapsed and fell into the river. It was foggy and visibility was poor.
On the mainland side of the bridge a lorry driver, sitting higher up and having a better view, noticed that the railing up ahead wasn't there, which struck him as strange, so he slowed down, and managed to stop in time. He closed the bridge from that side, but it took 40 minutes (in the days before mobile phones) before they were able to contact someone who lived on the other side of the bridge and they rushed down to set up barriers blocking access to the bridge on the other side.
I can still clearly remember the horror in the voices of the witnesses being interviewed on the news. They had stood in the freezing cold wind, and watched helplessly as headlights approached the bridge from the opposite side, and then plummeted down and vanished into the icy waters far below. It happened again and again. I don't remember how many cars they watched drop into the river, but 8 people died.
As a recently qualified driver, the thought of all those drivers, some perhaps with their families in the car with them, blithely driving across the bridge they drove across so often they could do it in their sleep, made a deep impression.
Since then I've driven through blizzards, bucketing rain and fog, but never at a speed that exceeded a safe stopping distance in the bit of road that I could see in front of me.