## 2 Literature Review  
### Environmental Benefits of Bikeshare  
The environmental benefits of bikeshare refer to the fact that bikeshare replaces other transport modes during the travel stage, which reduces VMT and fuel consumption, as well as greenhouse gas (GHG) emissions (e.g., CO\({}_{2}\) and NO\({}_{X}\)) [6; 27; 27]. In many studies, the environmental benefits of bikeshare are analyzed from the perspective of carbon emission reduction, with bikeshare regarded as a zero-carbon transport mode, the carbon dioxide emitted during travel by the transport modes that bikeshare replaces (walking, cars, and public transit) is quantified as the carbon emission reduction of bikeshare.  
Early studies of bikeshare travel often only looked at a few alternative transport modes and did not consider the full range of possible replacement options. [PERSON] et al. [27] considered that the environmental benefits of bikeshare in both reducing VMT and lowering GHG emissions depend mainly on bikeshare substituting for car travel and with less relevance to transport modes such as public transit, private biking, and walking. Similarly, [PERSON] et al. [28] believed that the environmental benefits of bikeshare are mostly achieved by substituting other high-carbon emission transport modes during the travel stage. [PERSON] and [PERSON] [6] set the travel distance threshold at 1 km and assumed that bikeshare travel shorter than 1 km could substitute for walking without environmental benefits and conversely substitute for car travel, resulting in environmental benefits. The results showed that bikeshare travel in Shanghai resulted in reduction of 8358 tons of gasoline, 25,240 tons of CO\({}_{2}\) emissions and 64 tons of NO\({}_{x}\) emissions in 2016. However, the study only considered bikeshare as a substitute for walking and cars, ignoring the environmental benefits of bikeshare replacing other transport modes.  
Subsequent studies have acknowledged that bikeshare can also replace public transit [29], and overlooking this fact may lead to an inaccurate assessment of the environmental benefits of bikeshare. To obtain more reliable results, related studies have started to incorporate public transit as an alternative mode when analyzing the environmental benefits of bikeshare. [PERSON] et al. [30] considered that bikeshare could replace walking, cycling,cars, and public transit and proposed a bikeshare carbon emission reduction estimation model (BS-EREM) to quantify the environmental benefits of bikeshare. [PERSON] et al. [7] studied the environmental benefits of bikeshare in two scenarios in Chengdu. In the first scenario, hypothetical bikeshare travel substituted walking and car travel. It is assumed that when the travel time is less than 3.87 min, bikeshare substitutes walking and vice versa substitutes car travel, which finds that the reduction in fuel consumption by bikeshare is 19,964.31 L, and the carbon emission reduction is 4125.13 kg. In the second scenario, it is hypothesized that bikeshare travel substitutes walking, car, bus, and metro travel, and the three relationships of substitution, integration, and complementation between bikeshare and public transit are identified based on the first scenario, which reveals that the reduction in fuel consumption by bikeshare is 13,198.68 L, and the carbon emission reduction is 2564.31 kg. [PERSON] et al. [26] analyzed the spatiotemporal characteristics of the carbon emission reduction benefits of bikeshare in Shenzhen and found that the carbon emission reduction of bikeshare within 500 m of the metro station areas accounted for 57.23% of the total carbon emission reduction of the whole day.  
It is worth noting that existing studies [6; 7; 22; 25; 26; 30] have focused on the use phase of bikeshare, considering that the carbon emission reduction benefits of bikeshare are generated by substituting other transport modes in the travel.