Impacts of high-speed rail projects on CO₂ emissions due to modal interactions: A review

This paper reviews existing literature on the CO2 emissions implications of high-speed rail (HSR) projects due to its interactions with air, road, and ordinary-speed rail. We conceptually classify the studies into three levels, with the first focusing on the emission comparison between HSR and the other modes, the second on the emission implication due to HSR-induced traffic reallocation, and the third on the life cycle assessment (LCA). We find that the literature is still in a relatively premature state. We also identify future research opportunities, including: i) to carry out a more detailed and comprehensive analysis regarding how HSR affects cargo operations of other transport modes and the corresponding CO₂ emission implications, ii) to further develop the game-theoretical models to be applied to estimate a fuller picture of modal splits and the corresponding CO₂ emission impacts, and iii) to apply LCA by considering the avoided life-cycle emissions associated with infrastructure and vehicles due to traffic diversion and the intricacies of modal interactions.