November 19th, 2019

by: Aminda Cheney-Irgens

​For readers not well acquainted with the rising carbon concentration in our atmosphere, I include the Keeling Curve, developed by Charles David Keeling. Why is this figure important? As we look at the x axis, showing the progression of time from around 1960 to the present day of 2019, and the y axis, demonstrating the parts per million of carbon in the atmosphere, a clear trend emerges: atmospheric carbon concentration is increasing.

Figure 1. Keeling Curve demonstrates the rise in atmospheric carbon concentrations from 1960-2019.

This isn’t a singularly reported finding, nor is it a common trend observed in the geologic history of our earth. The Intergovernmental Panel on Climate Change, Environmental Protection Agency, National Oceanic and Atmospheric Administration, NASA, and countless other agencies and researchers have asserted the same conclusion: the amount of carbon is higher than it has ever been before, and this is and will have drastic effects on our world and environments as we know them. Take a look at this next figure. We can see that throughout the ages, there has been a cycling of carbon, between green periods, when plant life takes carbon from the atmosphere, and ice ages, when carbon levels can increase. On the very far right, where the graph spikes up well above the dashed line, is where we are now. This represents the highest carbon concentration known to ever have occured on the planet! ​

Figure 2. Carbon concentration over the last 800,000 years.

 So what does public transportation have to do with atmospheric carbon? 
 
Limiting carbon emissions is important for our communities and our environment. There are many health risks associated with poor air quality in highly populated areas, many of which are due to increased traffic.3 According to the US Department of Transportation, “transportation accounts for 29 percent of greenhouse gas emissions in the United States,” which is over one fifth of our emissions.3 A study by the Transit Cooperative Research Program (TCRP), sponsored by the Federal Transit Administration, titled “Costs of Sprawl - 2000,” found that a main factor of energy usage growth in the U.S. is due to single occupant vehicles.3 
 
Use of public transit can curb this spike in carbon emissions. Public transit heavy rail systems such as subways and metros produce 76% less of a carbon footprint per passenger than when people choose to drive in their own cars, light rails have 62% less emissions per passenger, and bus transit creates 33% less (Check out Public Transportation’s Role in Responding to Climate Change (PDF)).3 According to the DOT, “public transportation encourages energy conservation, as the average number of passengers on a transit vehicle (10 for bus, 25 for a rail car) far exceeds that of a private automobile (1.6).” 3 
 
By sharing vehicles and investing in public transportation, we can address the carbon-heavy impact of single occupancy vehicles. The U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy states that “we already know that public transportation reduces pollution and eases congestion on the road,” an assertion supported by the United States Department of Transportation.3,4 This is also reflected in a 2004 study by ICF International which demonstrates that the use of public transit saved 947 million gallons of fuel that would otherwise have been used in private vehicles.3 As the DOE explains, “as communities become more sustainable, many transit fleets are switching over to cleaner, alternative fuels and technologies,” highlighting communities like Louisville, Kentucky that have switched to electric buses.4 
 
By encouraging the use of public transit, we can promote compact development, which means that less land is set aside for construction of roads and more is available for uses like parks, agriculture, and community development efforts.3 Simply by having fewer roads, contaminated water runoff reaching our water supplies is also decreased. This is supported by a study titled “Costs of Urban Sprawl,”  done by the Transit Cooperative Research Program (TCRP), sponsored by the Federal Transit Administration, stating that “compact development ...  can improve water quality through reducing the amount of impermeable surface runoff and preserve biodiversity through reducing fragmentation of natural habitat.” This same study asserted that “compact development could save the United States nearly 2.5 million acres of land.” Another study by the TCRP, titled “Transit-Oriented Development in the United States: Experiences, Challenges, and Prospects,” found that encouraging city development around the public transit networks can “reduce pressures to convert farmland and environmentally sensitive areas into housing and commercial development.” Not surprisingly, having greenspace is a crucial aspect of removing atmospheric carbon, and preventing the use of this land for road construction is important for addressing carbon emissions.  
 
But is it really worth it? 
 
To those who might argue that public transportation is not sustainable because so few people use it, I have news for you: you can change this! Take the initiative to find routes that can take you to work, to the mall, to museums, or other locations you frequent. There are countless routes that have been planned to drop off at convenient locations. Instead of paying attention to the road, you can take advantage of that time to get something else done (maybe that article you haven’t read for your class yet, or the book you just checked out from the public library). If you feel that the public transit in your community is not convenient, get involved in your local government, write your city council, and encourage the redesign of these routes so that they can actually serve the community!  
 
Many cities have successfully redesigned routes to have more buses run on frequently traveled days, and have fewer vehicles running on days when ridership is low. The issue many public transit planners run into is ensuring that routes are still accessible to those who rely on public transit, and this is extremely important if our public transportation is going to achieve the goal of being equitable  (Check out the article “The "Transit Isn’t Green Because It Runs Empty” Line” by Public Transit consultant Jarret Walker.)