Abstract: A process for tracking a user's use of available modes of transportation during a trip between an origin and a destination, the process comprising: generating a plurality of prospective trip plan (PTP) segments, the PTP segments being arranged into sequences that provide PTPs from the origin to the destination, each PTP segment being characterized by a transportation mode; collecting a travel data set comprising at least one travel measurement for each of a plurality of intermediary timepoints between the user leaving the origin and arriving at the destination; and determining a most probable time series of PTP segments traveled by the user based on an emissions matrix defining a probabilistic relationship between a PTP segment and a travel measurement, a transitions matrix characterizing a likelihood of the user transitioning from one PTP segment of the plurality of PTP segments to another, and the travel data set.