## 5 Conclusions  
As a new choice and an effective supplement to public transport, FFBS has an impact on people's choice of trip modes. This paper quantified the carbon emission footprint of FFBS, analyzed the modal shift patterns in response to different usage patterns of FFBS,  
Figure 4: Equilibrium point of FFBS. and estimated the break-even point based on the number of FFBS and the utilization of each bike, which is once a day on average. The results showed that the popularity of FFBS has brought positive environmental benefits. Additionally, the trip mode of using FFBS combined with public transport can replace motorized traffic more effectively with greater environmental benefits. The main conclusions of this study can be summarized as follows:  
* Through the questionnaire survey, it was found that the average riding distance of users was different under different usage patterns. The average riding distance was 2.3 km of using FFBS directly for short-distance trips. The average riding distance for users using FFBS to connect to public transport was 1.9 km. In addition, in the samples for Pattern 2, the frequency of respondents using FFBS was higher than that of respondents of Pattern 1. The complementary role of FFBS and public transport enhances the accessibility of both sides and provides users with a more convenient and efficient trip mode. * FFBS is not a zero-carbon transport tool. In its life cycle, GHG emissions will be generated in the production, operation, and disposal phases. A total of 76.710 kg CO\({}_{2}\)-eq emissions are generated for each FFBS. The production phase will generate the most CO\({}_{2}\) emissions, accounting for 70.67%. The environmental effect of FFBS is mainly achieved by replacing other high-emission transport modes in the use phase. In the sample of Pattern 1, nearly 80% chose other non-motorized modes or public transport modes as alternatives. In the sample of Pattern 2, 43.20% chose motorized traffic as alternatives. * When Nanjing has 257,000 FBBS and each FFBS is used on average once a day, the break-even point is about 227 days, which means the FFBS system can achieve a positive net environmental benefit. The amount of FFBS environmental benefits mainly depends on the modal shift and its use efficiency. When the turnover rate becomes higher, the environmental benefit will also be significantly improved. In sum, this paper provides some views on the environmental impacts of FFBS from the perspective of life cycle, but there are still shortcomings. We made assumptions about user behavior, which may lead to uncertainty of the results in order to get annual results. Additionally, how to combine intermodal survey data with historical trip data of FFBS is also a subject worthy of further study. In addition, with the popularization of new energy vehicles, modal shift patterns need to be considered more comprehensively in the future. The total amount of FFBS, use efficiency, and operation efficiency will still have an impact on the environmental benefits of FFBS, which is a great test for the government and enterprises. Therefore, it is still necessary to control the delivery of FFBS, reasonably plan the effective parking range of FFBS, improve the service level of FFBS near public transport sites, and introduce incentive measures to improve the proportion of users using FFBS to connect public transport. Future research could analyze measurement of the amount and the implementation of incentive measures, and consider the marginal effect of FFBS on other transport modes to provide more powerful support for the green development of FFBS. Conceptualization, R.L., X.M. and Y.J. ; methodology, R.L. ; formal analysis, R.L., F.Z. and X.M. ; investigation, R.L. and X.M. ; funding acquisition, Y.J. ; writing--original draft preparation, R.L. ; writing--review and editing, X.M., F.Z. and Y.J. All authors have read and agreed to the published version of the manuscript.