Opportunities for Scaling Up Energy Savings in Urban Rail Systems

As the world is becoming more aware of climate change's detrimental effects, it has become increasingly critical to implement changes in the sectors producing the highest levels of greenhouse gas emissions (GHG). The transportation sector is the highest contributor to GHG emissions in the United States. I have been taking the World Bank's e-learning course on Urban Rail Development. I learned that rail is one of the most energy-efficient and environmentally-friendly transportation options. In fact, according to the Washington Metropolitan Area Transit Authority, "...traveling by Metro results in 46% less GHG emissions per mile than driving in a single-occupancy vehicle." Despite this advantage that urban rail systems already hold over gas-powered vehicles, they still use a massive amount of energy. However, according to the International Energy Agency, urban rail networks are uniquely equipped to use energy from renewable sources because 75% of passenger rail relies on electric power. I wondered what measures could be taken to further improve upon the environmental advantages of urban rail systems. 

Energy storage systems (ESS) are also used to harness the energy produced by train braking. In an onboard ESS, trains temporarily store the energy produced by their own braking and later reuse it when accelerating. The use of rotating disks called flywheels has been implemented in onboard ESS in some urban rail systems. According to research by the University of Alberta, "...maximum energy savings of 31% can be achieved using a flywheel energy storage systems..." One such implementation of the flywheel mechanism in Bielefeld, Germany, produced savings of 360 MWh, which is 63 % higher than the predicted 220 MWh. 


Another way to harness the energy produced by breaking involves a stationary ESS; here, the energy produced from any train in the network breaking, to be transferred to an accelerating train in another part of the same track through a power supply line. This system would allow for significantly less energy to be wasted, extra energy to be consumed unnecessarily, and used efficiently in areas where it is needed. These systems work Studies have shown that ESSs can cut the overall energy consumption of an urban rail system by up to 45%. Additionally, there is evidence linking regenerative breaking in underground urban rail systems, similar to Metro, to lowering the HVAC system's energy consumption by reducing the heat load in tunnels and stations. The installation of ESS systems has proven to save money in the long run. Using less energy leads to lower costs, which is especially advantageous with today's rising energy prices.


Overall, in general, urban rail systems and trains are already one of the most energy-efficient and GHG emission methods of transportation because an overwhelming majority of these systems are already dependent on electric power, which opens up opportunities for obtaining this power from renewables sources. The installation of effective ESSs and flywheels can significantly cut back energy consumption and therefore costs, making this measure highly beneficial to the environment.



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