## 5 Discussion and Conclusions  
This study analyzed the operation characteristics of a free-floating bike sharing system as a feeder mode to rail transit in Beijing, considering space and time dimensions. This research was conducted by analyzing GPS data obtained from Mobike and urban morphology impacts. Further, the accessing distance was also analyzed. Several useful discoveries that may pertain to the planning and rebalancing of FFBS in Beijing are as follows:  
An obvious morning and evening rush hour in usage patterns of FFBS accessing rail transit on weekdays was observed. From the spatial-temporal dimension, FFBS access to rail transit has an obvious aggregating feature during rush hour. The spatial-temporal features indicate that during the morning rush hour, trips from the origin are first observed at the periphery of the city and then disperse, while trips to destinations are concentrated in the city center. An opposite trend is observed during the evening rush hour. Imbalanced usage of shared bikes was most likely to occur at stations near major residential areas in the city's suburbs and at stations near the city CBD located in the city center. The opposite trend is found during morning and evening rush hours. Compared to the uniform land use and low job-to-housing ratio around stations in suburban areas, rail transit stations in the city center have relatively high job-to-housing ratios, resulting in a one-way flow of commuting travel during morning and evening rush hours. Thus, it is indicated that for the rebalancing of bike sharing at night, more shared bikes should be placed near the residential areas (Cluster 3) in the suburbs of the city, as well as around the stations (Cluster 4) located in the city center. The imbalanced usage of shared bikes leads to parking problems. During the morning rush hour, many shared bikes pour into subway stations from residential areas. A similar phenomenon can be seen at the stations in the city center during the evening rush hour. The rapid concentration of shared bikes in a short period, along with disordered parking, indicates a requirement for the implementation and management of parking facilities around subway stations, especially in downtown areas with limited parking spaces. Allocation of sufficient and reasonable parking spaces for shared bikes around the target subway stations mentioned above is recommended, provided that public space resources are used fairly. Further, the assignment of personnel to coordinate and manage the shared bikes around the abovementioned stations during rush hours is also recommended. The urban morphology and location affect the accessing distance for bike sharing to rail transit. In city suburbs, travelers are more willing to ride longer distances to access rail transit, which indicates that it is reasonable to consider a wider bicycle service area in non-motorized environment planning and bike sharing planning around the stations. Simultaneously, creating attractive public transport and bicycle-friendly environments, and integrating bike sharing and high-quality public transport are critical to the new housing and office developments, which also makes sense to alleviate parking problems. This study analyzed the operation characteristics of Mobike as a feeder mode to rail transit in Beijing, which has significance as a reference for other cities integrating bike sharing and rail transit systems and solving the problem of the first or last mile. However, due to the limited access to data, this study analyzes only Mobike data, without consideration of the service conditions of other brands (such as Ofo, Bluegogo, etc.). In addition, the deviation of the GPS data of FFBS may impact the accuracy of analysis results to some extent. Although Mobike applies both GPS-based and base station-based positioning methods to improve the positioning accuracy, deviations are still unavoidable, especially when shared bikes are surrounded by buildings that interfere with signals.