## 2 Theoretical Background of Bike-Sharing Systems
### Definition and Classification of Bike-Sharing Systems  
Bike-sharing systems can be categorised based on their operational models, which determine how bicycles are accessed, utilised, and returned. This categorization represents the variety of design methods and the flexibility of bike-sharing in different urban context. The primary models include station-based systems, dockless systems, and hybrid systems.  
Station-based systems, often referred to as docking station systems, operate through fixed infrastructure where bicycles are both rented and returned. require users to collect and return bicycles at designated docking stations, strategically located in high-demand areas, such as transit hubs, commercial districts, and residential neighbourhoods. The permanent docking infrastructure ensures secure bicycle storage when not in use, thereby reducing the risk of theft and vandalism. This structure also facilitates efficient fleet management, as centralised docking points allow operators to monitor and reallocate bicycles effectively. While station-based systems offer reliability and operational control, they are less flexible, as users must find a docking station neat their point od departure or destination. Additionally, the installation and maintenance of docking stations can be financially demanding particularly in large metropolitan areas or cities with constrained public resources [3].  
In contrast, dockless systems eliminate the need for fixed docking stations, relying on GPS-enabled smart locks and mobile applications. These systems allow users to locate and access bicycles via smartphone apps and to park them anywhere within a designated service area. The flexibility of dockless systems enhances user convenience, enabling bicyclesto be picked up near the point of origin and dropped off close to the final destination. Additionally, dockless systems significantly reduce infrastructure costs, as they do not require the construction and maintenance of physical docking stations. However, this flexibility introduces several challenges, including improper parking, which can contribute to urban clutter, as well as increased risks of theft and vandalism due to the dispersed nature of the fleet. Operational inefficiencies may also arise when bicycles become concentrated in specific locations, necessitating active redistribution efforts by system operators [41].  
Hybrid systems combine elements of both station-based and dockless models, offering a balance between operational structure and user flexibility. These systems typically employ geofencing technology to create virtual parking zones, guiding users to park bicycles in predefined locations without the need for physical docking infrastructure. Hybrid models address certain limitations inherent in the other two systems by integrating the of predictability and order of station-based frameworks with the convenience and accessibility of dockless operations. They help reduce urban clutter by encouraging users to park in designated areas, while still allowing for pick-ups and drop-offs closer to users' desired locations. However, the implementing of virtual parking zones can be challenging, often requiring advanced technological solutions as well as effective strategies to ensure user compliance [2; 42].