## 4 Results
### GHG Emission Reduction Results
#### 4.2.3 Assessing the GHG Emission Reduction of Every FFBS Trip  
According to the survey results, the GHG emission reduction effect caused by FFBS in the use phase is estimated. As for the 1299 samples of Pattern 1, a total of 190.395 kg CO\({}_{2}\)-eq of GHG emission were saved during the use phase. While 34.90% of the samples did not generate GHG emission reduction in their FFBS trip, because they will use walking or other bikes for the trip, which do not generate GHG emissions in the use phase without FFBS. Most samples have an effective GHG emission reduction effect. Although FFBS has a low substitution rate for motor traffic in Pattern 1 samples, the reduction effect is still significant due to the high GHG emission factor of motor traffic. On average, the GHG saving using FFBS is about 63.726 g CO\({}_{2}\)-eq/p-km among the Pattern 1 samples. As for the 389 samples of Pattern 2, a total of 241.275 kg CO\({}_{2}\)-eq GHG emissions were reduced during the use phase. However, 15.17% of the samples increase GHG emissions. The reason is that if users do not use FFBS to connect the metro for the trip, they will turn to directly use bus or other non-motorized modes. In total, 39.85% did not reduce GHG emissions in the FFBS trip, because these respondents would still choose other non-motorized modes to connect the bus/metro without FFBS. In the sample of Pattern 2, the GHG emission reduction benefits mainly come from replacing the motor vehicle trip. In the Pattern 2 samples, about 300.718 g CO\({}_{2}\)-eq/p-km was saved, far greater than the average of samples for Pattern 1. The GHG emission reduction is about 118.329 g CO\({}_{2}\)-eq/p-km for the overall sample, which may be demonstrated as FFBS, as a supplement of the public transport, enhances the accessibility of public transport, and people are more willing to shift from high-emission motor transport to low-emission public transport. When FFBS is directly used for trips, because of the great influence of people's physical strength, which explains the short-distance characteristics of FFBS, the GHG emission reduction effect is not significant. Another study has shown that dock bike-sharing systems in different American cities reduce emissions by about 283 to 581 g CO\({}_{2}\)-eq per shared bike trip [37]. This may be due to differences in our modeling methods. In addition, there are differences in the traffic environment and trip characteristics of different cities. At the same time, we consider the trip chain of users, which will affect the final result. Considering the user heterogeneity, the respondent weighted factor is introduced to characterize the annual behavior of using FFBS. The result shows that the annual emission reduction benefits of FFBS in the use phase are 16.783 tons of CO\({}_{2}\)-eq in the sample for Pattern 1 and 24.470 tons of CO\({}_{2}\)-eq in the sample of Pattern 2. Then, according to the proportion of users with different use patterns obtained by the survey, when the number of FFBS users in Nanjing is 1.3 million, 76.96% of the users choose to use FFBS for a direct trip, and 23.04% of the users are used to connect the bus/metro. The existing norms stipulate that the mandatory retirement age of the FFBS is 3 years. When Nanjing has 257,000 FFBS, FFBS generate the net annual environmental benefits for Nanjing transportation sector by 25,195.921 tons of CO\({}_{2}\)-eq emission reductions in the life cycle. FFBS system has significant environmental benefits and effectively improves the traffic trip structure. However, most respondents only use FFBS for short-distance trips. In short-distance trips, most choose public transport and non-motorized modes as alternatives, so the environmental benefit is not significant. At the same time, in the sample of connecting trips, nearly half of the users are commuter trips, and more than 1/3 of them choose motorized traffic as alternatives. Therefore, strengthening the connection between FFBS and public transport is conducive to alleviating the impact of commuting at the trip peak.