Helen Fields:

Science, it turns out, backs up my love for the walking commute. For a study published earlier this year in the journal Preventive Medicine, researchers in the United Kingdom analyzed data from a study of nearly 18,000 British commuters. They found that those who walked to work were, psychologically speaking, better off than those who drove. People who took public transportation had more psychological wellbeing than drivers, too, although not as much as walkers.

Great article. She only forgot to mention that according to the study, the same health benefits also apply to those who cycle to work.