I knew this would be entertaining - I've purposely not responded just to see the range of reactions. I've decided to use jyl's calculations in which case I've commuted about 10,000 miles (kidding).

My question was the accepted definition of commuting and consensus seems clear - riding to and from work including side trips. While I'm essentially car free, commuting miles are not going to the grocery store or other rides.

Fwiw, I get plenty of vacation time, that's why I have leftover at the end of the year and will still carry over more than I'll use next year. Some day I'll take a sabbatical... maybe! The goal is not set in stone, but a big deal for me - 4,000 commuting miles is more than double my usual year. Thanks for all the feedback... sorta!