Most drivers will agree, getting home from work when it's raining takes longer. They will also admit that the same is true when it is dark, foggy or snowing.
The Highways Agency got a team of scientists from the University of Bristol to find out why, and they came to a remarkable conclusion: Headlights make cars slower.
"It is the only connecting factor," said head researcher, Ford Van Transit. "The correlation between headlight use and speed is remarkable."
In Volvos it is only possible to turn the headlights off by smashing them with a baseball bat, and any long distance, non-Volvo driving driver will testify that Volvos have the power to be a fast car, but inevitably drive slower than most invalid scooters. In Scandinavian countries where it is dark for a larger part of the year, there are less road traffic accidents per head than the UK because people drive slower due to their headlights.
Various hypotheses have been proposed to explain this counter-intuitive conclusion, with the two front runners being that headlights drain power from the car or that the the light itself is producing pressure on the air, making it more difficult to drive through. The latter seems more likely to the Bristol Researchers. The added pressure from the rear lights also seems to have a detrimental effect on speed, with so called 'brake lights' making some cars come to a complete stop.
"Oddly," said Van Transit, "when driving with only the front foglights on, despite there being no need for them, makes the car drive faster. We have seen this in numerous Novas and Corsas driven by young men."
The suggestion? Forget the headlights and use the front fog lights when it gets dark or rainy.