I have been biking 17 mile days for 4 months now and have yet to be able to do 5/5 days/week. I get physically fatigued so on those days I switch up my routine (good for motivation and safety) and take the bus/train in and car pool further with a colleague (because the mass transit system here does not run to my job). I do not drive a car because I do not have access to one so no choice to drive for moi. It causes more planning and dependance on others on my part, but that's part of the fun in learning to develop relationships with people and allowing yourself to depend on others is liberating, ironically.