it is just about that distance to my work as well (14mi) and yes i will ride it twice. for me thats really not that far so it really takes there and back to get in a good work out. i have found that its better for me to make my harder training rides when im not going to work and just use commuting to get some extra miles in. i will still ride at a good pace (18-20mph avg) but not all out before or after work. if i cant find time to ride during the week though i will take a longer more challenging route and hit it a little harder.