2.1.1. Car dependency and related impacts
For decades, private car has been the preferred mode of transport in urban contests. People enjoy travelling by car (Huwer, 2004), since, because of its flexibility (Habib et al., 2012; Kaspi et al., 2014;
Morency et al., 2012) and accessibility (Jorge and Correia, 2013), it is perceived as a transport means which can be adapted to every individual’s daily needs (Nobis, 2007). Furthermore, in a society characterized by individualized lifestyle (Nobis, 2007), private car is considered as a status symbol (Schmöller et al., 2015; Steg, 2005), i.e. car owners buy and use vehicles to show off identity, personality and social status (Webb, 2019). Moreover, in the past decades, the use of private car was encouraged (Schmöller et al., 2015). In addition, partly because of a growing urbanization (Mounce and Nelson, 2019), a lot of infrastructures were built in order to provide an efficient and quick flow of vehicles, deeply influencing the structure of urban areas (Burghard and Dütschke, 2019; de Lorimier and El-Geneidy, 2012; Schmöller et al., 2015). This results in a high car dependency (de Lorimier and El-Geneidy, 2012; Nobis, 2007), leading to an increasing car ownership rate experienced in many countries (Habib et al., 2012; Morency et al., 2012).
However a massive car usage has some negative externalities (Firnkorn and Shaheen, 2016; Jorge and Correia, 2013), producing serious impacts on citizens’ quality of life (Catalano et al., 2008).
Traffic congestion is an everyday problem in our cities (Carroll et al., 2017; Choudhury et al., 2017;
El Zarwi et al., 2017; Glotz-Richter, 2016; Habib et al., 2012; Lee et al., 2016; Lempert et al., 2019;
Morency et al., 2012; Shaheen and Cohen, 2007), particularly during peak hours when most of the people adopts private car to commute to work and to go to school (Carroll et al., 2017), often with low occupancy rates of vehicles (Choudhury et al., 2017). This causes high travel times for daily trips (Catalano et al., 2008; Jorge and Correia, 2013), which is subtracted from other activities (Jorge et al., 2015a), with implications even for the economy (Carroll et al., 2017). Moreover, the vast majority of existing cars on the roads are equipped with internal combustion engines powered by fossil fuels, thus negatively contributing to climate change (Burghard and Dütschke, 2019; El Zarwi et al., 2017).
Indeed the great diffusion of conventional private vehicles produces polluting and greenhouse gas emissions (Carroll et al., 2017; Catalano et al., 2008; El Zarwi et al., 2017; Firnkorn and Shaheen, 2016; Jorge and Correia, 2013; Kim et al., 2017a; Lee et al., 2016; Lempert et al., 2019) and an over-use of non-renewable resources (Burghard and Dütschke, 2019; Kim et al., 2017a; Lee et al., 2016;
Schlüter and Weyer, 2019), causing dangerous environmental problems (Kim et al., 2017b). In addition, since private cars are parked for about 95% of their lifetime (Kim et al., 2017a; Morency et al., 2015; Mounce and Nelson, 2019; Namazu et al., 2018), they contribute to reduce the limited availability of public space in urban contests (Firnkorn and Shaheen, 2016; Glotz-Richter, 2016;
Kaspi et al., 2014; Kim et al., 2017a; Shaheen and Cohen, 2007). Furthermore, high car traffic flows often produce a harmful effect of noise pollution (Carroll et al., 2017; Catalano et al., 2008). Finally, in the last years, car users had to experience the increasing of costs associated with the ownership and usage of cars (Jorge et al., 2015a), such as purchase, insurance and maintenance cost (Efthymiou et al., 2013; Jorge and Correia, 2013). In particular, the cost of fuels grew due to the general trend of energy prices (Efthymiou et al., 2013; Shaheen and Cohen, 2007), and parking costs raised due to the continuous reduction of public space (Clewlow, 2016; Shaheen and Cohen, 2007).
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2.1.2. Sustainable solutions
In order to overcome these drawback, policy makers implemented strategies to promote sustainable mobility (Clewlow, 2016; El Zarwi et al., 2017; Martin and Shaheen, 2011a, 2011b). In particular, the increasing awareness of environment (Carroll et al., 2017; Clewlow, 2016; Martin and Shaheen, 2011b) and the more restrictive rules about emissions (Habib et al., 2012; Morency et al., 2012; Shaheen et al., 2011), prompted authorities to adopt policies reducing the use of private vehicles, such as car-free zones, congestion charging and low emission zones (Mounce and Nelson, 2019), and to consider more sustainable travel means (Burghard and Dütschke, 2019; Clewlow, 2016;
Mounce and Nelson, 2019; Shaheen and Cohen, 2013). Among them, active modes, like walking and cycling can significantly reduce the carbon footprint (de Lorimier and El-Geneidy, 2012) and provide great flexibility (Huwer, 2004), however, they are not suitable for families and to carry goods (de Lorimier and El-Geneidy, 2012). Moreover, they are limited by distance and they require physical efforts (Huwer, 2004). On the other hand, traditional public transport is a sustainable alternative which can solve some of the previously described problems (de Lorimier and El-Geneidy, 2012; Jorge et al., 2015a; Jorge and Correia, 2013; Kim et al., 2017a). However, if compared to car, it has some drawbacks (Jorge et al., 2015a; Jorge and Correia, 2013), making a complete substitution of private vehicle very difficult. In detail, public transit does not provide enough flexibility for every trip purpose (Huwer, 2004), due to fixed scheduled frequencies (Jorge et al., 2015a) and limited operating periods (Kaspi et al., 2014). Moreover, it requires high investment costs (Jorge et al., 2015a) through public resources, and it does not guarantee the privacy of passengers (Kaspi et al., 2014).
Furthermore, it often has limited service areas (Jorge et al., 2015a; Jorge and Correia, 2013; Kaspi et al., 2014) and accessibility (Kim et al., 2017a), thus generating troubles for people living far from a public transport station or stop (Kaspi et al., 2014). Therefore, due to these disadvantages, users still prefer ravelling by private car (Kaspi et al., 2014).
2.1.3. Car sharing and its advantages
Considering these drawbacks, car sharing can fill the gap between private car and public transport (Efthymiou et al., 2013; Kaspi et al., 2014; Morency et al., 2007), since it allows users to enjoy the privacy and flexibility of private car (Barth and Shaheen, 2002; Clewlow, 2016; Zhou and Kockelman, 2011) without directly bearing all the associated costs (Cooper et al., 2000; Costain et al., 2012b; de Lorimier and El-Geneidy, 2012; de Luca and Di Pace, 2015; Efthymiou et al., 2013;
Efthymiou and Antoniou, 2016; Hua et al., 2019; Huwer, 2004; Jones and Leibowicz, 2019; Kim et al., 2017a; Martin and Shaheen, 2011a; Shaheen et al., 2006; Shaheen and Chan, 2016; Shaheen and Cohen, 2013; Yoon et al., 2017) and constraints (Coll et al., 2014). From this point of view, car sharing is considered a mix between private vehicle and public transit (Habib et al., 2012; Morency et al., 2012), since it provides the same freedom and advantages of the former (Martin and Shaheen, 2011a) with affordable prices (Barth and Shaheen, 2002; Priya Uteng et al., 2019), like the latter.
Furthermore, car sharing is a sustainable transport mode (Lagadic et al., 2019; Priya Uteng et al., 2019), since it potentially reduces car ownership (Catalano et al., 2008; de Luca and Di Pace, 2015;
Jin et al., 2018; Lempert et al., 2019) and the number of private vehicles required to satisfy the total travel demand (Barth and Shaheen, 2002; Morency et al., 2015), thus increasing the availability of public space (Barth and Shaheen, 2002; Catalano et al., 2008; Huwer, 2004; Lagadic et al., 2019) and reducing traffic congestion (Lee et al., 2016).
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Moreover, car sharing vehicles are often equipped with low-polluting engines (Barth and Shaheen, 2002; Catalano et al., 2008), such as electric power (Burghard and Dütschke, 2019). In addition, it encourages the adoption and the future purchase of private electric vehicles (Cartenì et al., 2016; Schlüter and Weyer, 2019). In this way, car sharing can decrease greenhouse gas emission (Jorge et al., 2015b; Lempert et al., 2019; Martin and Shaheen, 2011b; Rabbitt and Ghosh, 2013).
Furthermore, car sharing can change mobility habits (Barth and Shaheen, 2002; Le Vine et al., 2014a;
Zhou, 2012), since users are more aware of the cost of driving (Catalano et al., 2008; Efthymiou and Antoniou, 2016; Zheng et al., 2009). For instance, car sharing increases the use of public transport (Lempert et al., 2019), providing a complementary travel mode (Clewlow, 2016). Therefore car sharing offers the opportunity to contribute to sustainable urban development (Jorge et al., 2015a), without forcing travellers to forgo the advantages of driving a car (Huwer, 2004). According to this point of view, car sharing does not delete car usage, but it makes users aware of how properly using a vehicle (Coll et al., 2014; de Lorimier and El-Geneidy, 2012; Huwer, 2004; Morency et al., 2015).
Even if car sharing cannot provide users with exactly the same benefits of private vehicles (Priya Uteng et al., 2019), compared to a past context where private car, public transport, taxi, bike and walking where the main travel means (Becker et al., 2017c), nowadays car sharing is a new mobility option (Barth and Shaheen, 2002), which allows users to choose the transport mode which can best accommodate their mobility needs (Becker et al., 2017c; de Luca and Di Pace, 2015; Huwer, 2004;
Jorge et al., 2015a).
2.1.4. Car sharing diffusion
The first car sharing implementation took place in Switzerland in 1948 (Becker et al., 2017a;
Shaheen et al., 1999; Shaheen and Cohen, 2007), however only in recent years car sharing has become widespread (Clewlow, 2016; Lempert et al., 2019; Morency et al., 2015), becoming an usual mobility option throughout the world (Costain et al., 2012b; Shaheen and Cohen, 2007), even in Italy (Rotaris et al., 2019). Besides to the previously explained advantages of car sharing, its rapid growth was due to the diffusion of Information and Communication Technologies (Becker et al., 2017a; Clewlow and Mishra, 2017; Lempert et al., 2019; Morency et al., 2015; Standing et al., 2019). In particular, Global Positioning System and communication network allow users and operators to trace the position of a shared vehicle (Kaspi et al., 2014; Shaheen and Chan, 2016); this information is made available anywhere and whenever needed (Kaspi et al., 2014). Moreover, car sharing is an element of the sharing economy (Glotz-Richter, 2016; Jin et al., 2018), which is penetrating even in the transportation sector (Jin et al., 2018). Indeed, according to this perspective, car sharing decreases the demand of new products and increases the use of existing ones, since it offers the possibility to go on using (shared) car, whenever needed (Huwer, 2004), without purchasing a new private vehicle (Jin et al., 2018). Finally, many young adults living in developed countries decide to postpone to acquire a driving licence (Mounce and Nelson, 2019); this suggests that owning a car is gradually becoming less important (Schmöller et al., 2015). These reasons foster the shift from car ownership to “car as demand” (Firnkorn and Müller, 2012; Kent and Dowling, 2016a; Mounce and Nelson, 2019).
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2.1.5. The role of the public sector
Due to the recent diffusion of car sharing, policy makers have to face its importance both as a new mobility option for users and as a new market opportunity for operators. From the first point of view, local authorities should manage the relationship of car sharing with other existing transport means (Terrien et al., 2016; Welch et al., 2018), such as public transport (de Luca and Di Pace, 2015;
Firnkorn and Müller, 2011). Properly integrating car sharing in planning policy (Glotz-Richter, 2016;
Lagadic et al., 2019) towards a Mobility as a Service (MaaS) perspective (Lagadic et al., 2019), they can offer users the best combination of mobility opportunities that can accommodate all their mobility needs (Firnkorn and Müller, 2011), in terms of flexibility and accessibility (Huwer, 2004). Moreover, considering previously explained advantages, policy makers should promote car sharing as a means to reach sustainability goals (Habib et al., 2012; Lagadic et al., 2019; Morency et al., 2012). From the second point of view, local authorities have to discuss with car sharing operators in order to address public resources towards the implementation of a car sharing program (Ceccato and Diana, 2018;
Shaheen et al., 2006). In particular, policy makers can decide to provide financial support (Lagadic et al., 2019) or to fix fares in order to reduce competition with public transport (Gordon-Harris, 2016;
Mounce and Nelson, 2019). Moreover they can allow public parking spaces (Becker et al., 2018;
Dowling and Kent, 2015; Gordon-Harris, 2016; Kent and Dowling, 2016b; Lagadic et al., 2019; Le Vine et al., 2014b, 2014a; Mounce and Nelson, 2019; Shaheen et al., 2011; Stasko et al., 2013; Terrien et al., 2016), the use of public transit reserved lanes or free access to limited traffic areas (Ceccato and Diana, 2018). Furthermore, they can indicate the location of charging infrastructures for shared electric vehicles (Gordon-Harris, 2016; Mounce and Nelson, 2019). Finally, local authorities have the possibility to promote car sharing to citizens (Stasko et al., 2013), in order to foster its diffusion (Lagadic et al., 2019).
In order to provide sound basis for local authorities, as a support for policies, which promote and manage car sharing (Ceccato and Diana, 2018), this new travel mode has to be introduced in travel demand modelling. In this way, it is possible to forecast and to quantify the effects of car sharing on travel behaviour (Becker et al., 2018; Dias et al., 2017; Martin and Shaheen, 2011a) and, consequently, on the transport system, environment (Terrien et al., 2016) and society (Namazu et al., 2018; Rotaris et al., 2019).