## 4 Data Analysis
### Spatiotemporal Patterns
#### 4.2.1 Kernel Density Analysis  
The kernel density tool of the ArcGIS software is adopted to calculate the variation distribution density of the trips from origin and trips to destination of Mobikes. Selecting 1 h as an interval, the traffic volumes of the two types of trips around subway stations during weekdays are reflected simultaneously on maps, as illustrated in Figure 3. In these maps, red represents that the number of Mobikes undertaking trips from origin to the rail station is higher than trips from this station to destination, indicating that more bike-sharing demand flows into the rail station than out; green represents the contrary.  
Figure 2: Diurnal curves bike sharing trips for accessing rail transit stations: (**a**) Trips on weekdays vs. trips on weekends; (**b**) Trips from origin vs. trips to destination.  
Generally, in the morning rush hour (from 6:00 to 10:00), trips from origin (red) increase and then dissipate on the city outskirts; trips to destination (green) gradually increase in the city centers, as illustrated in Figure 3a. From 6:00 to 7:00, trips from origin at subway stations on the outskirts start to increase, and are apparently higher in number than those in the city center. A majority of these areas are located around large-scale residential districts in the urban periphery. A longer commuting distance prompts commuters to depart from their home earlier. After 8:00, trips from origin on the outskirts begin to dissipate, while trips to destination start to increase in the city center. Approximately 1 h after departing from their residences, a large number of commuters arrive at their offices in the city center. After 9:00, this phenomenon gradually dissipates as the majority of the commuters have completed their commuting trips. It is noteworthy that region A in the figure is in a perpetual state of high level of trips from origin. It is the central business district (CBD) of Beijing; therefore, many employment positions, highly intensive mixed land development, and abundant transportation facilities attract millions of people here daily. Meanwhile, the Guomao subway station in the regional center is the busiest transfer station in Beijing with an average passenger flow of 300,000 daily. Bawangfen bus station is 1.8 km from the Guomao subway station. Each day, 350,000 commuters from the eastern suburbs transfer to other modes of transport at this bus station to enter the city in the morning rush hour. Many of them opt to proceed to the Guomao station to change to the subways, and Mobike is a reasonable option for connecting the two. The regions where green is relatively prominent in Figure 3a (from 8:00 to 9:00) include Zhongguancun Science Park (region B), Olympic Common Domain (region C), Financial Street (region D), Lize Financial Business District (region E), and Cultural Circle of the Temple of Heaven (region F). These five regions are major functional zones that accommodate Beijing's cultural, financial, scientific, and technology industries with many jobs. In this regard, many commuters shift to Mobikes here to arrive at work in the morning rush hour.  
During evening rush hour, a state contrary to the morning condition appears, as illustrated in Figure 3b. A large number of commuters return to their residences on the outskirts of the city. Compared with the morning rush hour, the integral color of the figure is lighter, indicating that the rush-hour travel lasts longer and is dispersed to a higher degree.  
Figure 3: Spatiotemporal activity patterns of the Beijing Mobile during the rush hours on weekdays: (**a**) Morning rush hours; (**b**) Evening rush hours.