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Mitigating CO2 emissions from long-haul commercial trucking is a major challenge that must be addressed to achieve substantial reductions in greenhouse gas (GHG) emissions from the transportation sector. Extensive recent research and development programs have shown how significant near-term reductions in GHGs from commercial vehicles can be achieved by combining technological advances. This paper reviews progress in technology for engine efficiency improvements, vehicle resistance and drag reductions, and the introduction of hybrid electric powertrains in long-haul trucks. The results of vehicle demonstration projects by major vehicle manufacturers have shown peak brake thermal efficiency of 55% in heavy-duty diesel engines and have demonstrated freight efficiency improvements of 150% relative to a 2009 baseline in North America. These improvements have been achieved by combining multiple incremental improvements in both engine and vehicle technologies. Powertrain electrification through hybridization has been shown to offer some potential reductions in fuel consumption. These potential benefits depend on the vehicle use, the details of the powertrain design, and the duty cycle. To date, most papers have focused on standard drive cycles, leaving a research gap in how hybrid electric powertrains would be designed to minimize fuel consumption over real-world drive cycles, which are essential for a reliable powertrain design. The results of this paper suggest that there is no "one-size-fits-all" solution to reduce the GHGs in long-haul trucking, and a combination of technologies is required to provide an optimum solution for each application. [ABSTRACT FROM AUTHOR]

• Greenhouse gas emissions of bike rebalancing was considered for helping understand the induced environmental impacts. • Bike Sharing System-Rebalancing Emission Estimation Model (BSS-REEM) was proposed. • Greenhouse gas emitted by rebalancing vehicles was estimated for urban bike sharing system. • Bike rebalancing was positively correlated with cycling and fluctuated considerably throughout the year. • Using human-power or electric tricycles to assist diesel trucks in dispatching bicycles helped reduce emissions. 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 tCO 2 -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 tCO 2 -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 environmental evaluation of BSSs, providing a basic for their sustainable management. [Display omitted] [ABSTRACT FROM AUTHOR]

• Compressed natural gas-based hybrid electric truck model is developed and optimized based on real cycles. • Well-to-Wheel analysis is applied to figure out the methane leakage and carbon dioxide equivalent emissions. • The same methodology is applied to North America, Europe and China to make a comparison. Following the tendency of sustainable development, compressed natural gas as an alternative fuel has been expanded applied in the transportation sector these years. Although several studies on the life cycle are quite comprehensive for passenger vehicles, it is problematic to apply these results to heavy-duty electric hybrid trucks. This study applies the Well-to-Wheel methodology on compressed natural gas fuel. The optimized hybrid electric truck model is built up to minimize the truck performance variation. The total CO 2 equivalent emissions and the methane leakage as indicators are compared among the three largest emitting countries. The results indicate that compressed natural gas-based hybrid trucks have 9.1%–18.7% less CO 2 equivalent emissions than diesel-based ones and the results are more obvious for heavy-duty trucks. Nevertheless, this advantage may be minimized by methane leakage, particularly in the recovery process, accounted for 7.3% Total CO 2 equivalent emissions increase in North America, 5.1% in Europe, 5.3% in China from well to wheel. Applying natural gas in hybrid electric trucks does have environmental benefits. Methane capturing and compression efficient improving can be the faster ways to help reach the emission reduction target. [ABSTRACT FROM AUTHOR]