Our study of Jetty in Mexico City assessed the journeys its users would otherwise make and the empty travel needed to provide the service
Methods
A large user survey recorded trip legs, previous travel options and reasons for choosing Jetty’s shared cars, vans and buses. These responses defined a counterfactual for each passenger: the combination of modes and distances they reported they would otherwise have used. We compared those avoided vehicle kilometres with the kilometres operated by Jetty, then varied vehicle occupancy and empty running in sensitivity tests. This allowed the analysis to distinguish kilometres shared among passengers from additional positioning or low-occupancy travel.
Findings
In the study’s preferred scenarios, shared vans reduced vehicle travel by approximately 0.2–1.1 km per passenger. Shared cars increased it by 7–10 km per passenger, and buses by 0.4–1.1 km per passenger. The sensitivity analysis showed that these results depended on occupancy, the amount of empty running and the modes passengers would otherwise have used. Carrying several passengers was therefore insufficient on its own: a shared service could still increase traffic when it substituted for public transport or required substantial additional vehicle movement.