On the asymmetric relationship between car sharing membership and car ownership levels: Insights from the German Mobility Panel

Car sharing is one of the shared mobility services that can potentially cause a reduction in car ownership. The topic has been extensively addressed in the literature, yet existing evidence is mainly based on observations related only to car sharing subscribers, or cross-sectional surveys targeting a representative sample of the drivers’ population at best. Since car ownership is influenced by a wide array of socio-demographic factors beyond car sharing, the association between car ownership levels and car sharing membership needs to be validated. To this effect, the present paper resorts to the 2012/2013 until 2020/2021 waves of the German Mobility Panel (MOP), an unbalanced and rotating (the same individual is interviewed in no more than three consecutive waves) annual panel survey. This study presents the results of the annual survey in which there was a steady growth in sample sizes, starting from 1173 households and 2369 individuals being interviewed in 2012/2013, up to 1963 households and 3461 individuals in 2020/2021. A treated group of car sharing subscribers is identified and related car ownership levels are compared with those of a control group that was created through propensity-score-based matching, controlling for a wide array of socio-demographic variables. Observed differences are still strong and they can therefore be safely associated with car sharing membership. Additionally, the panel nature of the data allowed for studying the patterns of car sharing subscription and unsubscription together with the changing levels of car ownership within the observation period. An asymmetry of behaviors clearly emerged, since the observed decrease in car ownership when subscribing to car sharing is much stronger than an increase when unsubscribing. By leveraging those results and projecting them to the whole universe (German car drivers), it is shown that the net balance in terms of number of cars taken out of German streets by existing car sharing systems undergoes significant changes. These changes occur according to subscription and unsubscription patterns, even when the annual growth rate of subscribers is fixed. Some additional scenarios are finally proposed assuming different annual subscriber growth rates, according to recently observed trends.