This paper reports on a natural experiment, which studied groups of commuters who are equivalent in most important demographic respects, and who had equivalent commuting experiences, but were differentially affected by a new and improved mass transit (rail) route to work. These commuters changed a significant aspect of their commute, but did not change other critical aspects of their lives (e.g., the start and end points of the trips, the jobs they go to, the homes they return to), so that commuting changes were not confounded with other life changes. This study also provided the opportunity to experimentally study - and longitudinally follow – the impacts of this major change in travel time and number of mode transfers in a much more controlled fashion than has been possible heretofore. In addition to this longitudinal study of actual commuters, we also conducted a true experiment using student subjects as simulated commuters, sending them on trips that were identical to those taken by our real commuter subjects, to see if these effects could be replicated under these controlled, even if somewhat more contrived, conditions.