In the heart of Saudi Arabia, a high-speed railway is not just connecting two of Islam’s holiest cities, but also serving as a testbed for innovative climate solutions. The Haramain High-Speed Railway (HHR), stretching 450 km between Makkah and Madinah, is at the center of a groundbreaking study published in the journal “Frontiers in Sustainable Cities” that could reshape how we think about decarbonizing transport in fossil-dependent economies.
The research, led by Hafiz Abdul Wajid, presents the first comprehensive evaluation of the HHR’s CO2 mitigation potential. By examining operational and energy-related factors, the study offers a nuanced look at how high-speed rail (HSR) systems can contribute to climate goals. “The key insight is that occupancy rates and energy sourcing are not independent factors; they interact in complex ways that can significantly influence emissions outcomes,” Wajid explains.
The study employed a dynamic scenario-based mathematical modeling approach, considering variables such as train energy efficiency, grid emission factors, renewable energy adoption, and occupancy rates. The findings are striking: in the worst-case scenario—low occupancy and a fossil-heavy grid—the HHR could result in a net increase of 187 kilotons of CO2 annually compared to buses. However, in the best-case scenario—high occupancy and 100% renewable energy—the system could achieve savings of 285 kilotons of CO2 per year, equating to a saving of 11.93 kg per passenger for the entire journey.
One of the most compelling findings is the outsized influence of occupancy rates on carbon performance. “Ridership optimization can yield greater emissions reductions than renewable energy integration alone, particularly when grid decarbonization is partial,” Wajid notes. The study identifies critical thresholds: net CO2 savings are achieved when occupancy exceeds 70–75% under the current grid mix, or 45–50% when renewable energy adoption reaches 50%.
These insights are particularly relevant for Saudi Arabia’s Vision 2030, a comprehensive plan to diversify the economy and promote sustainable development. By integrating operational variability and passenger behavior, the methodology provides a practical toolkit for aligning clean energy investments with ridership incentives. “This research offers a roadmap for transport planners and policymakers to make informed decisions that balance economic and environmental goals,” Wajid adds.
The study also contributes to the United Nations Sustainable Development Goals (UN-SDGs) 9, 11, and 13, which focus on industry, innovation, sustainable cities, and climate action. By establishing a foundational reference for future research on decarbonization thresholds in HSR systems, the research could have far-reaching implications for Middle Eastern and arid-region contexts.
For the energy sector, the findings underscore the importance of integrating renewable energy sources with operational efficiency measures. As countries worldwide grapple with the challenge of decarbonizing transport, the HHR’s experience offers valuable lessons. “The interplay between energy sourcing and ridership dynamics is a critical factor that must be considered in any decarbonization strategy,” Wajid concludes.
As the world looks to transition to a low-carbon future, the Haramain High-Speed Railway stands as a beacon of innovation and a testament to the power of data-driven decision-making. By unlocking the climate potential of high-speed rail, this research could pave the way for a more sustainable and resilient transport sector.