## 1 Introduction
Nowadays, all modern and advanced bike-sharing systems (e.g., Velib' Metropole, Velo'v, Santander Cycles, Bicing, Villo) use mobile apps, which greatly facilitate the users by providing them useful information and facilitating the process of getting and returning a bicycle from/to the bike stations. More specifically, the mobile apps of those systems provide to the users services such as (a) finding the nearest station, (b) information about the availability of free bikes and free docks in every station in real-time, (c) confirmation of the successful return of a bicycle to a station, (d) routing, (e) information about the rentals that a user has conducted, as well as charts showing their progress, (f) subscribing or renewing their subscription to the system, (g) evaluating the quality of the specific bicycle, (h) evaluating the quality of the path that they used for their trip. Also, many of the mobile apps of those systems include gamification features in order to gather useful data from the users, engage them in the system and utilizing them in the bike-redistribution process. An essential prerequisite for the success of bike-sharing systems is the change in behavior of commuters, in order to shift to active modes of transport, such as cycling. According to the literature, the use of bicycles for daily commuting is to a large extent correlated to the attributes of:  
* Cities: cycling usage levels are higher in cities with greater density and intense mix of land use [9; 10]. The prevailing weather conditions [11], as well as the topography of a city [12], also have a significant impact on the levels of bicycle use. * Infrastructure: the existence of appropriate infrastructure and in particular bicycle lane networks providing safe and comfortable movement, in any destination, is a key factor for bicycle use [13], especially for commuters with limited cycling experience [14]. Except for the bicycle lane networks, it is also of great importance to form safe and secure parking spaces for bicycles, to provide cyclists priority at signalized intersections and to implement restrictions for private cars [15]. * Trips: bicycles are considered to be preferable for short daily trips, but not shorter than one kilometer, since in this case it can be easily replaced by walking [16]. Also, it has been shown that when the final destination is near to the city center, bicycle use is more likely to be preferred [17]. * Travelers: in countries with limited cycling experience and less developed cycling culture, it has been identified that males and especially those of a young age are more likely to choose cycling for commuting. However, it should be mentioned that in well-established cycling cities, no differentiations based on gender or age can be found [18; 16]. Private car ownership and attitudes towards cycling are also two aspects of great importance [17]. In some of the abovementioned factors, transport planners can intervene with the aim to promote cycling as a transport mode for daily trips. Also, it is of great significance to implement actions targeting to attract and engage travelers in the use of bicycles. According to [PERSON], there are three types of cycling promotion actions [19]: (a) information activities and awareness-raising campaigns, (b) targeted training and educational programs, and (c) individualized promotion. For maximizing the benefits of implementing those cycling promotion actions, it is very useful to cluster the travelers in groups with similar attributes and common needs in order to prioritize them based on the probability to shift to cycling and at the next stage to approach them with the appropriate messages. The categorization of the travelers can be based on characteristics, such as (a) gender, (b) age, (c) area of residence, (d) area in which he/she works, (e) bicycle ownership, (f) frequency of bicycle use, (g) purpose of bicycle use, (h) attitude towards other available transport modes [20]. [PERSON] et al.