I literally started commuting because I was training for a triathlon. I was frustrated because I was blowing off a lot of my bike workouts that I had scheduled for the evening. I'd ride the bus home and sit on the couch and never make it back outside. I had this genius idea that if I had my bike with me at the end of the work day I'd be forced to ride it and I might as well do the workout I had planned.

I started bike racing about 10 years ago and most of my training is still either on the way to or from work. My suggestion though is not to do the same route every day. Even if you don't do regimented interval training, you'll have better results if you switch things up. I've got routes that add 10 to 30 miles to the direct path between home and the office. Some days those might be highly structured and some days are just riding the ride and listening to a ball game in one ear bud.