Writing a blog presents a sore temptation to rant about things. I have been very restrained until now; I have not yet mentioned Cambridge cyclists, the (mis)guided bus, Brexit or Trump. However, I reserve the right to visit any or all of these topics at some point in the future. Nevertheless, on this occasion I feel the need to make an important point in the interests of road safety and my sanity.
The fact is that many drivers do not seem to know how to use their rear fog lights legally, safely and with due consideration for other road users. Some drivers switch them on at the first sign of mist and leave them on for several days, presumably in case the mist returns unexpectedly. Others, I can only assume, switch them on by accident at some point, and then spend months wondering what that curious orange light on their dashboard is for.
Rear fog lights should be;
used only in foggy conditions - not rain, spray or snow
used only when visibility is 100m or less* - this is pretty thick fog which we do not see very often
switched off when visibility improves
Note that the use of rear fog lamps is not mandatory - the use of headlamps in conditions of bad visibilty, is.
The Road Vehicles Lighting Regulations 1989 actually state their use is prohibited "at any time other than in conditions of seriously reduced visibility". This is defined in the Highway Code, Rule 226, as 100m or less.
Rear fog lights dazzle following drivers and mask brake lights and indicators, (Highway Code, Rule 236). Consider turning them off when the vehicle behind you is obviously close enough to see you without them. That will improve their vision of the road ahead and make your brake lights and indicators clearer. In short, it is in the interests of your own safety.
Driving in heavy fog is difficult and requires intense concentration. Please do not increase the burden on other drivers by thoughtless use of rear fog lights.
There - rant over!