外文文献翻译原文及译文标题：用于共享单车系统优化设计的连续近似模型文献出处： Sustainable Cities and Society， Volume 52, January 2020, pp:1-19译文字数：5300多字原文A continuous approximation model for the optimal design of public bike-sharing systemsSoriguera Francesc，Jimenez EnriqueAbstractDuring the last decade, public bike-sharing systems have gained momentum and popularity. Many cities worldwide have put their trust in bike-sharing to promote bicycle use and move towards more sustainable mobility. This paper presents a parsimonious model from which to derive the optimal strategical design variables for bike-sharing systems (i.e. the number of bicycles, the number of stations and the required intensity of rebalancing operations). This requires an integrated view of the system, allowing the optimization of the trade-off between the costs incurred by the operating agency and the level of service offered to users. The approach is based on the modelling technique of continuous approximations, which requires strong simplifications but allows obtaining very clear trade-offs and insights. The model has been validated using data fromBicingin Barcelona, and the results prove, for example, the existence of economies of scale in bike-sharing systems. Also, station-based and free-floating system configurations are compared, showing that free-floating systems achieve a better average level of service for the same agency costs. In spite of this, the performance of free-floating systems will tend to deteriorate in the absence of a strong regulation. Furthermore, if electrical bikes are used, results show that battery recharging will not imply an active restriction in station-based configurations. In conclusion, the proposed modeling approach represents a tool for strategic design in the planning phase and provides a better understanding of bike-sharing systems.Keywords: Bike-sharing, Electric bike, Facility location problem, Rebalancing, Optimization, Continuous approximation, Bicing-BarcelonaCities around the world envisage huge potential in cycling as a sustainable alternative to motorized individual mobility. The bicycle, as an urban transportation mode, accounts for a marginal modal share in many cities, while most of the urban trips could be done efficiently, in terms of time and costs, by cyclingHeinen, Wee, and Maat (2010). In such contexts, cycling could reduce motorized traffic and curtail pollutant emissionsCao and Shen (2019), promoting an environmentally sustainable and socially equitable transportation system, together with a healthier way of lifeJain and Tiwari (2016).Public bike-sharing programs stand out as one of the most ambitious initiatives taken by transportation authorities to promote cycling in cities. The bike-sharing concept is simple: take the bike for your trip and leave it behind for others when finished. Benefits for the user are multiple, including the release of all the burdens of ownership (i.e. investment, maintenance, storage, etc.) and the liberty and flexibility of one-way trips, not worrying about the bicycle once at the destination. Bike-sharing also provides a convenient alternative to walking for the first- and last-mile segments in multimodal tripsLu, Hsu, Chen, and Lee (2018). Pioneer implementations (e.g.White Bikesprogram in Amsterdam, The Netherlands (1965);Vlos Jaunesin La Rochelle, France (1974); Green Bike Schemein Cambridge, UK (1993); orBycyklenin Copenhagen, Denmark (1995) allowed understanding that in order to reduce the exposure to theft and vandalism, both the user and the bike needed to be clearly identified. This, together with technological progress, gave rise to the currently most accepted framework of public bike-sharing systems, based on bicycle docking at stations and electronic membership cards (known as 3rd generation or station-based systems; seeDeMaio (2009)orShaheen, Guzman, and Zhang (2010)for an extensive review of the past, present and future of bike-sharing programs). In this type of systems, it is only at stations where members can pick-up or return bicycles. Implementations frequently referred to are Wuhan (90,000 bikes) or Hangzhou (78,000), being the largest station-based systems in the world, and also ParisVelib(20,600), BarcelonaBicing(6000), or MontrealBixi(5200). More recently, the introduction of GPS devices and advanced locks in shared bikes entailed new opportunities for the original concept of free-floating bike-sharing (i.e. station-less). Since 2015, free-floating initiatives have appeared around the world, and with special intensity in China. For example,MobikeandOfo, the two largest operators in China, rolled out 280,000 shared bikes in Shanghai and 200,000 in Beijing as of June 2017; by the end of 2017, these fleets had raised to 2.35 and 1.5 million respectively with a total of 15 operating companies. This explosive growth implied that globally, 150 Chinese cities were served by free-floating systems in 2017, wit