When I started commuting two and a half years ago on my MTB with knobbies, my goal was to find the shortest route to work/home. In the begining it was 12.5 miles. Later my friend discovered a couple of shortcuts that cut it down to 11.3 miles. No matter what form of transportation I use, I like to go fast, so I swapped the knobbies for street tires. Over the next year my speed increased and I kept riding the same route. In a quest for greater speed, I bought a road bike and immediately knocked a couple of minutes off the commute. This year I'm trying to rack up more miles so the commute has gone from 11.3 to 13.5 to 20 miles one way. I do have to leave the house a bit earlier in the morning but that isn't a big deal.