I have a similiar commute - 20 miles each way (give or take depending on route). Half my commute is rural country roads (where I live) and half is more urban/suburban. I had grand expectations that when we moved out here, I'd do this commute all the time and eventually work up to doing every day.

Turns out, I don't. It's not really the miles (which one can absolutely adapt to), it's the time. I just can't spare 3+ hours on the bike EVERY DAY.

In addition to the ideas that Indigoiis suggested, I also do a half/half commute. I drive to work with my bike, ride home, ride back the next day and then drive home. This way, I'm only on the bike 1.5 hours per day which is much more manageable.