Developing Sustainable Bike Share Systems 

Abstract
Bike share is viewed as a sustainable transportation mode and has been gaining popularity in many cities. However, having a bike share system, regardless of a station-based, dockless, or a hybrid one, does not guarantee that it is sustainable and provide environmental benefits. Many factors, including the bike and station material manufacturing and disposal, the bike rebalancing using automobiles, and the transportation modes replaced by the bike share trips, determine whether a bike share system is making contributions in reducing the transportation energy use and emissions. Existing research evaluating the life cycle environmental performance of bike share systems often has two limitations: 1) relying on system average data instead of program specific data and 2) focusing on the existing system setup instead of optimizing the system design and operation. However, different bike share programs in different cities have different number of bikes and stations, are operated with different rebalancing strategies, and have different pricing models that may impact the bike share usage and transportation mode substitution. It is important to conduct life cycle assessment on bike share systems using program specific data. Additionally, the existing system may not have the most suitable setup for the city. Because bike share is still an emerging transportation mode, the quota on how many bikes an operator can place in a city is often developed based on simple rules and lack scientific support. Evaluating how different system design and operation setup may impact the system environmental performance is critically needed. This research aims to fill both of these gaps.

Using a data driven approach, we are evaluating the bike share systems in several cities in the U.S. and China to quantify their environmental impacts. We conduct life cycle assessment of each system using program specific bike, station, bike share trip, and bike rebalancing data collected from each system. We also consider the historic travel pattern in that city to infer the transportation mode substituted by bike share to estimate the net greenhouse gas emissions reduction from each bike share system. Additionally, we have also proposed a framework to optimize bike share system design and operation from the life cycle’s perspective, integrating system simulation and optimization methods. When a system has more bikes, it will require less rebalancing. This will reduce the use phase environmental impacts with the cost of increased upstream and downstream impacts. Our proposed framework will evaluate this tradeoff between bike fleet size and rebalancing frequency to identify the optimal system design and operation strategy from the life cycle environmental benefits’ perspective.

Our preliminary results show that (1) most of the bike share systems are currently oversupplied with more bikes than needed; (2) decreasing bike fleet size through more frequent rebalancing will increase the system’s life cycle GHG emissions; and (3) choosing appropriate rebalancing fleet size, loading capacity, and setting multiple depots can reduce a BSS’ rebalancing GHG emissions. Our study results can inform policy and decision making to help develop shared economy systems that achieve sustainability goals.