Mass transit is often portrayed in a positive light, juxtaposed with gas-guzzling automobiles. Proponents of this mindset, such as the American Public Transportation Association (APTA), an interest group that advocates for the expansion of public transit, argue that public transportation is the “most effective strategy available for reducing energy consumption and improving the environment.”
While public transit can play a role in reducing energy emissions, this perspective fails to offer nuance or contextualize the current state of public transit to serve large, broad audiences. In certain cases, automobiles might actually create less environmental harm than public transit.
APTA’s 2002 report on public transit and environmental conservation claims that, “For every passenger mile traveled, public transportation produces only a fraction of the harmful pollution [greenhouse gasses] of private vehicles: only 5 percent as much carbon monoxide, less than 8 percent as many volatile organic compounds, and nearly half as much carbon dioxide and nitrogen oxides.” APTA draws this conclusion by comparing private vehicle emissions to public transit. These calculations have several limitations, however, as the study lumps together data from passenger miles and fuel emissions for buses and rails located in metropolitan areas while excluding data for buses and rail lines that travel outside metropolitan areas. APTA also leaves out ferry boats (known to be energy intensive), trolleys, intercity buses and air travel in its calculations. Additionally, the study makes no reference to variations in vehicle fleet fuel efficiency standards, which have been steadily rising due to technological innovations in the automobile industry and increases in Corporate Average Fuel Economy (CAFE) standards.
Studies that harp on the environmental benefits of public transportation when compared with automobiles also often underestimate transit ridership rates relative to vehicle occupancy rates. As transportation consultant Thomas Rubin states in his critique of a paper, “Public Transit Buses: A Green Choice Gets Greener” published by the Center on Globalization, Governance & Competitiveness, calculations of fuel efficiencies in public transit predicated on the assumption that buses operate at full capacity do not depict actual ridership rates, which are declining.
Mr. Rubin noted that the authors calculate greenhouse gas emissions by establishing the average bus size capacity, 70, as a baseline for transit ridership rates. The Center on Globalization, Governance & Competitiveness’ study then measures the average output of CO2 for buses per 100 passenger miles and asserts that automobiles with a fuel efficiency of 25 miles per gallon emit 89 pounds of CO2, whereas buses release 14 pounds.
Rubin counters this assumption, noting that the center’s study does not account for increases in vehicle fuel efficiency standards, nor does its conclusion reflect average transit ridership rates of 9 passengers per trip, a decrease from 12 passengers per load in 1977. Ridership rates in metropolitan areas also rarely reach 70 passengers, with the 2017 average for metropolitan trips being 38 passengers per trip. This center’s figure therefore grossly misleads the audience to believe that buses are almost always more efficient than cars.
Unfortunately, transit ridership is projected to continue to decline, despite active efforts on the part of transportation agencies to market public transit to the general public. During the period of 2017 to 2018 alone, US transit ridership decreased 2.7 percent. This is due, in part, to increased suburban sprawl, high vehicle ownership rates, and the surge in popularity of ridesharing apps like Uber and Lyft. As it currently stands, just five percent of the population relies on public transportation to commute to work.
While studying at California Institute of Technology as an undergraduate, Resnick Institute graduate fellow John Naviaux measured CO2 emissions released by Orange County Transportation Authority’s (OCTA) bus fleet to determine the environmental impact of public transportation. In his thesis, “From Cars to Buses: Using OCTA Ridership to Analyze the Emission Benefits of Bus Transportation,” Naviaux studied OCTA bus routes over a period of several weeks and collected weekday bus trip data on passenger ridership rates, boarding information, geographical location, and distance traveled for those routes from 7 am to 1 pm local time. He noted that estimates would likely fluctuate had he collected data during the weekends or times of off-peak demand as well.
Naviaux found that OCTA buses emit less CO2 per passenger mile compared to a vehicle with a fuel efficiency standard of 22.5 miles per gallon and one occupant per vehicle, producing a savings of 20,000 to 50,000 tons of CO2 per year. Certain routes fared better than others, however. He notes that bus routes with low ridership rates offered only slightly reduced emissions when compared to emission rates of private vehicles. Buses also incurred “dead miles,” or the miles traveled while not actively providing services on assigned routes. In the case of Orange County, approximately 20 percent of miles measured during the study were dead miles. Unfortunately, dead miles were not included in his environmental efficiency calculations. Ultimately, Naviaux asserts that fuel-efficient vehicles can reduce emissions at a similar rate to buses, especially when there is more than one passenger in the car.
Additionally, OCTA buses are more environmentally-friendly than the standard bus fleet. This is due to its higher than average ridership rates of 14.49 passengers per trip (compared with the national average of 7 passengers) and the use of liquid or compressed natural gas to operate. This limits the applicability of this experiment results to help determine the environmental impacts of other bus fleets across the country. Furthermore, the fact that OCTA limits its bus route operation to times of peak demand also helps to reduce its carbon footprint.
When buses and trains run half empty, public transit can be more environmentally harmful than automobiles. Trains are often lauded as being one of the most environmentally efficient forms of transportation. In his policy report, “Does Rail Transit Save Energy or Reduce Greenhouse Gas Emissions?” Cato Institute Senior Fellow Randal O’Toole challenged the myth that rail transit is more energy-efficient than other modes of transportation. He noted that while rail is powered by electricity, the manner in which cities harvest electricity, as well as ridership rates, influence the degree to which railways emit CO2 and other harmful gases per passenger mile. For example, Washington, D.C., Massachusetts, and Ohio generate electricity by burning oil, while three-fourths of Washington state’s electricity is sourced from hydroelectric dams.
By analyzing data available on the average number of pounds and BTUs of CO2 emitted per passenger mile along various modes of transportation, O’Toole found that the Toyota Prius, the most fuel-efficient vehicle on the market, “uses less energy than other forms of travel, but generates about the same CO2 as heavy rail and commuter rail.” The Prius emits 1,659 BTUs of energy and 0.26 pounds of CO2 per mile. Comparatively, the average automobile releases 3,885 BTUs and 0.61 pounds of CO2. When accounting for national average ridership rates, heavy rail emits 2,600 BTUs and 0.25 pounds of CO2 while light rail averages 3,465 BTUs and 0.36 pounds. Motor buses are the least energy efficient by this metric, releasing 4,365 BTUs and 0.71 pounds of CO2.
Assuming fuel efficiency standards continue to increase at a rate of 2.7 percent a year, O’Toole argued that the fuel efficiency rates of rail lines being planned and constructed would need to surpass the automobile fuel standards that will be in place 25 to 30 years from now in order to be more environmentally efficient than private vehicles at that time. This is partially due to the fact that the lifetime of a railway following 10 years of planning and construction is typically 30-40 years. If they fail to do so, it is possible that the fuel efficiency standards of cars will exceed that of rail lines in the near future.
This does not mean that there isn’t a role for public transportation to play in reducing emissions. But depoliticizing transit funding is a crucial step in ensuring that transit development is done in an eco-friendly manner. Far too often, politicians have perverse incentives to propose and expand public transit in areas with low ridership demand in order to hold ribbon-cutting ceremonies or in hops of gaining popularity among select constituents.
Investments in mass transit ought to be more selective and focused on expanding and maintaining ridership in areas with high rates of transit ridership by operating more heavily during times of greater demand. In cases where ridership is low, reducing shuttle sizes and getting rid of unpopular lines altogether can substantially reduce emissions. Exploring alternative fuel options to diesel such as compressed natural gas or electricity would also help curb pollution.