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| Fig. 1. CO2 emissions per passenger-mile for NYC Subway versus gasoline cars. (Image source: N. Wang.) |
In a world where emissions and environmental sustainability are receiving increasing attention, large cities offer clear examples of how transportation choices shape energy use. New York City is especially useful to study because its dense population relies heavily on mass transit. This paper compares the energy use of the New York City Subway with gasoline cars. Using publicly available electricity and ridership data, I estimate the subways energy requirement in kWh per passenger-mile and contrast it with typical automobiles. The goal is to show how much energy the subway saves and explain why these savings occur.
The New York City Subway is a vast rapid-transit network that spans four of the city’s five boroughs (Manhattan, Brooklyn, Queens, and the Bronx) and operates 24 hours a day, 7 days a week. The MTA subway map shows a dense web of underground, elevated, and at-grade routes, especially outside Manhattan, linking major residential and commercial centers. [1]
Power is delivered via an electrified third rail, carrying 625 volts DC; subway cars draw electricity through a sliding shoe that contacts the rail, supplying power for motion, lighting, and station systems. [1] NYSERDA reports that the system uses dedicated traction power substations and modern rolling stock with regenerative braking, which allows trains to return a portion of their braking energy back to the third rail. [2]
NYSERDA’s traction-energy analysis estimates that the NYC Subway consumed approximately 1.5 × 109 kWh of traction electricity in 2021. [2] The same study shows that modern subway trains return a meaningful portion of braking energy to the system. On average, a train uses about 25.8 kWh per stop and returns about 5.4 kWh of regenerative braking energy to the third rail, roughly 16% of total traction energy. [2] Regenerative braking captures part of the kinetic energy during deceleration and returns it to the power system, reducing net energy demand.
Annual traction electricity is taken from NYSERDA’s system analysis, which reports 1.5 × 109 kWh consumed by the subway in 2021. [2] To translate this into an energy intensity per passenger-mile, I use the Federal Transit Administration’s National Transit Database agency profile for MTA New York City Transit. For heavy-rail service (the subway), the 2022 profile lists approximately 7.06 × 109 annual passenger-miles traveled. [3] Dividing traction electricity by subway passenger-miles gives energy use per passenger-mile.
Automobile energy use and occupancy values are drawn from the University of Michigans Personal Transportation factsheet. In the United States, average vehicle occupancy has declined over time and was reported at approximately 1.5 persons per vehicle-mile in recent years. U.S. light-duty vehicles also show improving fuel efficiency, with the average new vehicle fuel economy reaching about 27 miles per gallon for the 2023 model year. [4] Using the standard lower heating value of gasoline, 33.7 kWh per gallon, this corresponds to approximately 1.25 kWh of energy per vehicle-mile. [4] Dividing by the average occupancy yields an energy intensity of roughly 0.83 kWh per passenger-mile for light-duty automobiles. [4]
Using 1.5 × 109 kWh of traction electricity and 7.06 × 109 passenger-miles yields a subway energy intensity of about 0.21 kWh per passenger-mile. For automobiles, the FHWA values of 27 miles per gallon and 1.5 passengers per vehicle give an energy intensity of about 0.83 kWh per passenger-mile. Thus, the NYC Subway uses roughly four times less energy per passenger-mile than typical light-duty vehicles. As shown in Fig. 1, this energy advantage also leads to substantially lower CO2 emissions.
Using a representative grid emission factor of 0.37 kg CO2/kWh, the subway produces about 0.079 kg CO2 per passenger-mile, or roughly 80 g. [5] Applying the same factor to automobile energy use (0.89 kWh per passenger-mile) gives about 0.33 kg CO2 per passenger-mile, or about 330 g. In other words, for the same passenger travel, cars emit a little more than four times as much CO2 as the subway.
The results show that the NYC Subway operates with much lower energy use and emissions per passenger-mile than private automobiles. NYSERDA’s detailed measurements confirm strong regenerative braking performance, with trains returning around 16% of traction energy to the third rail. [2] This energy recovery contributes directly to the subway’s overall efficiency.
However, energy efficiency is not what primarily drives rider choice. People rely on the subway because it is cheaper, faster, and more convenient than driving in dense urban conditions. In New York, the economic and spatial structure of the city aligns personal convenience with energy efficiency. This supports the broader idea that transportation behavior follows costs and convenience rather than physics alone, and that well-used mass transit can provide both mobility and substantial energy savings.
© Nathan Wang. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "New York City Subway Map," New York Metropolitan Transportation Authority, 2025.
[2] K. Cummings, "Subway System Energy Usage and Electrical Storage System Applications Analysis," New York State Energy Research and Development Authority, September 2022.
[3] "2022 Annual Agency Profile: MTA New York City Transit," New York Metropolitan Transportation Autority, 2022.
[4] "Personal Transportation," Center for Sustainable Systems, University of Michigan, September 2025.
[5] "Cost Estimate: H.R. 521, the First Responder Fair RETIRE Act," U.S. Congressional Budget Office, September 2022.