Clocks change this weekend (from British Summer Time to Greenwich Mean Time) in the UK, and as usual we get a bunch of silly stories about how we ought to change this practice (for example BBC News - Putting clocks back damages our health, says expert). I'm a cycle commuter, and personally I think increased darkness in the morning would be a dangerous change.  I'm not convinced drivers are fully awake during the morning commute - a suggestion supported in the article by Dr David Lewis, a chartered psychologist who has done research into the effect of sunshine on our well-being

"But there is a danger that people leaving for work in the morning don't really wake up properly if it's not light."

It is apparently recommended that adults take 30 minutes exercise per day and children take 60 minutes.  It does seem to me that the easiest way of getting this exercise is by encouraging people to commute by bike where possible (and take public transport with its attendant walking to/from buses and trains): I expect people are less likely to do so in the dark.