Life-cycle greenhouse gas emission assessment for bike-sharing systems based on a rebalancing emission estimation model

Bike sharing is regarded as a green transportation mode, while the existing studies on its greenhouse gas (GHG) emission assessment seldom consider bike-rebalancing process. In this research, a Bike Sharing System- Rebalancing Emission Estimation Model (BSS-REEM) was proposed to conservatively quantify historical GHG emitted by rebalancing vehicles. Taking the largest bike sharing system (BSS) in North America as a case, we comprehensively assessed its life cycle GHG footprint considering the system's infrastructures, rebalancing process and cycling activities and analyzed the GHG reduction benefits of using pedal and electric trikes to assist trucks in dispatching bikes. Results showed that the bike rebalancing activity level fluctuated throughout 2020 and 56.1% of bikes were dispatched by vehicles and the rest driven by customers' incentive mechanisms. The annual conservative GHG emission of bike rebalancing was 92.1 tCO2-eq when merely diesel trucks were used. Such emissions would be reduced with trikes to assist rebalancing. The emission reduction driven by riding in 2020 reached 14,333.6 tCO2-eq, representing 1.8 times of the entire system's GHG emissions over its service life. Quantifying GHG emissions of the bike-rebalancing process promotes a systematic and comprehensive envi- ronmental evaluation of BSSs, providing a basic for their sustainable management.