What an informative thread. Thank you all (well nearly all). We have regularly driven late Friday evenings from London to Glasgow at this time of year and have always been fascinated by the skyline, especially from midnight on when we hit Cumbria and continue on through Scotland. There is usually very little traffic on the motorways so it is a joy to drive on the roads and still be able to see the outline of the hills etc. I will now have a better understanding of what is happening.