Ride-sharing -the combination of multiple trips into one -may substantially contribute towards sustainable urban mobility. It is most efficient at high demand locations with many similar trip requests. However, here we reveal that people's willingness to share rides does not follow this trend. Modeling the fundamental incentives underlying individual ride-sharing decisions, we find two opposing adoption regimes, one with constant and one with decreasing adoption as demand increases. In the high demand limit, the transition between these regimes becomes discontinuous, switching abruptly from low to high ride-sharing adoption. Analyzing over 360 million ride requests in New York City and Chicago illustrates that both regimes coexist across the cities, consistent with our model predictions. These results suggest that current incentives for ride-sharing may be near the boundary to the high-sharing regime such that even a moderate increase in the financial incentives may significantly increase ride-sharing adoption.
RESULTS
Contrasting ride-sharing adoptionCurrently, only a small fraction of people adopts ride-sharing even in high-demand situations, despite all its positive aspects [26]. For example, among more than 250 million ride-hailing requests served in New York City in 2019 less than 18% were requests for shared transportation [27]. Moreover, the city's ride-sharing activity varies strongly across different parts of the city, in particular at locations with a high number of ride-hailing requests (see Fig. 1): For instance, in the East Village and Crown Heights North the fraction of shared ride requests is relatively high, while it is low at both John F. Kennedy and LaGuardia airports, locations that would intuitively be especially efficient for sharing rides. Several other location throughout New York City as well as Chicago exhibit similarly contrasting