The relationship between public transport and ride-hailing services has not been extensively studied.
Ride-hailing, exemplified by companies such as Uber, Lyft, Grab, a Singapore-based company, and DiDi Chuxing, which is based in China, has transformed how people can get around with on-demand rides made easily available. This has likely also created changes to how we use public transport, but that relationship has only recently been more extensively studied.
In a recent paper using DiDi data, which was made accessible to researchers, it was determined that in a major city in China (Chengdu) about 33% of rides requested on the ride-hailing application could be substituted by public transport. In fact, during the day the rate is higher, and particularly higher near the city center and near underground stations.
Using three different regression models, ordinary least squares, spatial autocorrelation, and zero-or-one inflated beta regression, the researchers looked at origin and destinations of rides relative to the transport network in the city and determined the rates at which rides could be substituted.
Housing prices seem to have a strong relationship as to why people take rides that could be substituted. In other words, people who live in more expensive areas tend to utilize ride-hailing services when, in fact, they could have used public transport.
Economically disadvantaged, on the other hand, attempt to utilize public transport even when peripheral areas are accessed, which are poorly covered by public transport.
The implication is integrating public transport with ride-hailing could potentially help make traffic more efficient. Inequalities in access to smartphone-based ride-hailing services means that a large portion of the population is less able to access services where ride-hailing could better cover more peripheral transport regions.
Making ride-hailing available through other means than smartphone-based technologies and without the need for credit cards could potentially expand lower income utilization of these services.
In another study looking at ride-hailing, pollution, congestion, and energy consumption all increase due to ride-hailing use.
However, ride-hailing also has benefits, including rider-matching services that can quickly match services with riders, reduce parking requirements, and enables car-free households to move around more easily.
Overall, however, similar to the study in Chengdu, ride-hailing does not appear to be as complimentary to public transport as cities might hope but often it appears to substitute for it. Similarly, better integration between ride-hailing and public transport could potentially better or at least more effeciently utilize the advantages of public transport and ride-hailing.
Furthermore, at least for some, that ride-hailing could act as a substitute for car ownership, although in general congestion seems to increase, suggesting that the effect of ride-hailing likely increases the number of cars on roads.
Another study looked at ride-hailing in a more complex way, specifically the types of transport that ride-hailing has the most impact on in 273 cities in China. This study showed that bus rides decrease as people begin to use ride-hailing applications more.
On the other hand, rail use increases when ride-hailing is used along with rail. This suggests people are substituting relatively slower transport with ride-hailing, while ride-hailing does have the potential to complement transport systems by increasing the speed of trips.
Similar results, interestingly, were seen when people used bike-sharing within cities. This has implications for cities in that they may need to improve the speed of services to help reduce traffic congestion and put more incentives for bus services, while, similar to the other studies, also integrating ride-hailing with public transport better.
What studies appear to suggest is that ride-hailing is not likely to help traffic in areas, at least certain traffic, in that it could be causing more congestion and likely more pollution. However, ride-hailing does have the potential to benefit transport by being better integrated with public transport and when it services are used along with more rapid rail services.
Cities may want to consider also how ride-hailing could better service areas with poor transport and low access to ride-hailing services. In fact, better ride-hailing and transport integration could make the entire transport system more efficient.
 For more on how ride-hailing services could affect the use of public transport, see: Kong H, Zhang X and Zhao J (2020) How does ridesourcing substitute for public transit? A geospatial perspective in Chengdu, China. Journal of Transport Geography 86: 102769. DOI: 10.1016/j.jtrangeo.2020.102769.
 For more on the effects of ride-hailing on traffic, public transport, pollution, car rides, and other effects, see: Tirachini A (2020) Ride-hailing, travel behaviour and sustainable mobility: an international review. Transportation 47(4): 2011–2047. DOI: 10.1007/s11116-019-10070-2.
 For more on using ride-hailing and different modes of public transport, see: Shi X, Li Z and Xia E (2020) The impact of ride-hailing and shared bikes on public transit: Moderating effect of the legitimacy. Research in Transportation Economics: 100870. DOI: 10.1016/j.retrec.2020.100870.