• We provide causal evidence about motivations to carpool. • Carpool is preferred for non-urgent trips. • Placing carpool as the default choice in non-urgent trips increased demand by 8% • For urgent trips, single-occupancy rides are preferred. • For urgent trips, carpooling can still be motivated by messages and defaults. Carpooling within taxi services presents a sustainable alternative to single-occupancy vehicles, given the rapidly growing urban population and reliance on private cars. Aiming to examine passenger choices for this type of carpooling and their underlying motivations, we experimentally tested mock-ups mimicking DiDi, China’s biggest ride-hailing provider. We conducted a 4 × 2 between-subjects experimental design (N = 1600) comparing the effects of three motivational messages – environmental benefits, carpool safety, and monetary savings (vs. no message control group). Furthermore, we tested the effect of placing the carpool option as the (default) first option shown to participants (vs. the second option), when choosing their preferred ride, both for an urgent trip, and a non-urgent trip. Results showed that carpool was preferred for non-urgent trips, and placing carpool specifically as the default choice in non-urgent trips further increased average demand by 8% (4% without any additional message). For urgent trips, single-occupancy rides were preferred. However, even in the case of urgency, adding a motivational message or placing carpooling as the default first option significantly increased carpool choice.
Zhang et al. (2026) studied this question.