## 1 Introduction  
In the last few years, there is a great debate about micro-mobility schemes, which are constantly gaining ground. It seems that these schemes have a great role in the transport systems of many cities around the world. One of the most popular and historic micro-mobility schemes is the bike-sharing systems, for which many different definitions have been used. According to the European Cyclists' Federation, a bike-sharing system is defined as \"a self-service, short-term, one-way-capable bike rental offer in public spaces, for several target groups, with network characteristics\" [1]. A more illustrative explanation is provided by [PERSON] et al. (2016) who, among others, describe bike-sharing as a system where \"users access bicycles on an as-needed basis for oneway (point-to-point) mobility and/or roundtrips\" and also distinguishes two main bike-sharing categories, the station-based and the free-floating [2]. The first bike-sharing system operated in 1965 in the city of Amsterdam [3]. This system, which became known as \"White Bikes\" because of the color of the bicycles, failed extremely quickly due to the complete absence of rules. However, this system was the starting point for the development of many new systems, which by their characteristics are classified in the following four generations [3; 4]:  
* 1 st generation, \"Free Bike Systems\" or \"White Bikes\": its name originates from the \"White Bike system in Amsterdam. The failure of this generation is attributed to the vigorous phenomena of vandalism and theft, which are the result of complete anonymity and lack of surveillance. * 2 nd generation, \"Coin-Deposit Systems\": they owe their name to the fact that bike rental in this generation's systems was carried out through coin deposit in the stations. The coin was returned to the user after completing the rental. These systems firstly appeared in Danish cities in 1991 and the establishment of the Bycyklen system in Copenhagen was a landmark. As in the case of the first generation systems, the anonymity of the users resulted in frequent phenomena of vandalism and theft. * 3 rd generation, \"Information Technology-Based Systems\": through the utilization of information technology, it was sought to collect data about the rentals and the users. Bike-sharing systems launched smart cards or mobile phone applications, through which the rental process was being done. Advertising companies (Clear Channel, JCDecaux) had a significant contribution to the growth of such systems and the establishment of the Velo'v system in Lyon can be considered as an important milestone. * 4 th generation, \"Demand Responsive, Multi-Modal Systems\": the characteristics of this (current) generation are not clearly defined, but it is anticipated that the main attributes that will differentiate it from the third generation are the following: (a) integration with other sharing systems (e.g., car-sharing, scooter-sharing) and public transport, (b) further utilization of technology (e.g., usage of GPS devices for bicycle tracking, usage of electric-assist bicycles), (c) improved methods and algorithms for the re-distribution of bicycles, (d) flexible/mobile stations, which can be relocated according to the usage patterns or total absence of stations (dockless systems). It should be mentioned that the international experience has shown that specific regulations are needed for the dockless systems since they can cause important defects within the built environment [5; 6]. The history of the evolution of bike-sharing systems shows that European cities led the developments to a large extent. The history of the North American and Asian systems is much shorter, but they are growing rapidly over the last few years [7; 8]. What is more important, the presentation of the four generations makes obvious that Information and Communications Technologies (ICT) played a significant role in the evolution of bike-sharing systems.