Reply to Lopez et al.: Sustainable implementation of taxi sharing requires understanding systemic effects

Extract

We have recently developed a method that allows the quantification of spare capacity in urban taxi systems through trip sharing (1), hence making it more efficient and less resource intensive—all other things being equal—in particular fares, which can be modified by public policy. In their comment on our study, Lopez et al. observe that a complete evaluation of the environmental sustainability of taxi sharing requires not only considering direct impacts, but also indirect impacts (2). We fully agree with this observation. For limiting the scope of our analysis (1) to a manageable extent, and in lack of an established methodology for quantifying the impacts of vehicle sharing at the granularity of single trips, we were not able to account for effects that can be considered as exogenous to the taxi system. Indeed, urban and regional models are composed of both exogenous and endogenous variables, and “much of the ongoing research agenda can be focused on transferring variables from the exogenous to the endogenous category” (3). The extensions suggested by Lopez et al. (2) and in our report (1) go exactly along this direction.