I'm lucky, work for smart people who realized that if they wanted me to sign they had to yield on where. (Or as they put it: we don't understand what you do anyway and we trust you, so whatever you want as long as you show up most of the days.)

Edit: Used to work on personal projects in a previous job that included long commutes. For me it is often the best time of the day for programming: Nobody to interrupt, few distractions, a very specific start time and stop time.