Commuting to work by bike can be a great way to improve your health. For me - it's a way of getting exercise into my day without having to sweat it out at the gym. If my only option for exercise was the gym - I just wouldn't do it, that's not the sort of person I am. Cycling to work doesn't feel like exercise though - it feels like getting to work. It's like sneaking puréed veg in with your kid's mash potato at tea time.
My commute is just over five miles, which takes about half an hour. When I first started cycling to work and planning my route, I was really surprised as to just how little you need to use the road. In addition to the cycle lanes we're all familiar with, there's all kinds of cycle ways, canals and other routes you can take, which avoid the major roads. Quite often, these routes are shorter/faster than taking the road.
I think one of people's major worries about cycling to work (other than traffic) is probably the weather. I'll be honest - when it's windy, it sucks, but it's not that windy that often. I've not found the rain to be that much of a problem either. If it's wet outside, I'll wear waterproofs, but during my commute it rarely rains during those exact 30 minutes that I'm outside, even in winter.
So, if you're like me and need to be tricked into exercising the way a fussy child would be, try taking up cycling to work. A lot of employers now offer cycle to work schemes where you can save money on the purchase of a bike and spread the cost out over 12 months interest free.