|Fig. 1: This bar chart breaks down the energy provided from each energy source to each of these five major mass transit systems. Each system uses two to three hundred gigawatt-hours of energy annually, with the primary energy sources being diesel and electricity. [1-6] (Source: E. Martin)|
When Bay Area workers plan their commutes, they are rarely presented with quantitative information on how much energy they would save using mass transit instead of driving. These data are scattered over a variety of sources, but they are available. [1-6] They show that five major Bay Area transportation systems use about half as much energy annually as people who live in San Mateo County and drive to work alone.
Our transportation systems use energy in many forms: gasoline, diesel, B5 and B20 biodiesel, natural gas, propane, and electricity. To compile all these fuel sources into one energy measurement, we have to say how much energy is in a therm of natural gas, a gallon of diesel, gasoline, propane, or biodiesel, or a kilowatt-hour of electricity. The units used to express energy from different sources can vary wildly.  For example, the energy available in 1 tonne of oil is approximately equal to 400 therms of natural gas, or 12,000 kilowatt-hours of electricity. However, if we look at gallons of fossil fuel sources or a therm of natural gas, they come out to roughly the same amount of energy, as seen in Table 1.
|Table 1: Various sources of energy are converted into an equivalent number of kilowatt-hours of electricity. |
Table 2 summarizes the energy use of the region's largest public transportation systems: BART, VTA, Caltrain, AC Transit, and SFMTA. [2-6] The breakdown of energy provided by each source for each system converted to equivalent kilowatt-hours of electricity is shown in Fig. 1. In total, these systems use 1294 gigawatt-hours of energy annually. Note that Caltrain figures were only available for diesel use. Caltrain stations do use electricity, but these numbers were not available and have not been included in this estimate.
A typical monthly home electricity bill is somewhere in the hundreds of kilowatt-hours, so as individuals, we rarely think about quantities of energy as large as thousands of gigawatt-hours.  To put this in context, there are roughly 462,000 people in San Mateo County between the ages of 18 and 64. If we assume that 60 percent of them drive to work, that is around 277,000 drivers. Assuming these drivers use an average of 1 gallon of gas for each of 250 working days per year, they use the equivalent of 2330 kilowatt-hours of electricity. This means that just the commuters living in San Mateo County who drive to work use nearly twice the energy of all the major Bay Area public transportation systems combined, which operate every day of the year and serve approximately 350,000 commuters in addition to other riders.
|Table 2: Each of these systems reported energy use in various forms. Within a factor of two, these systems each use roughly the same amount of energy. [2-6]|
© Eileen Martin. 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.
 "BP Statistical Review of World Energy," British Petroleum, June 2015.
 R.A. Sfeir and S. Chow, "Energy Efficiency Assessment of Bary Area Rapid Transit (BART) Train Cars," Base Energy, Inc., BASE-PGE-05-09, November 2007
 "2013 Sustainability Report," Santa Clara Valley Transportation Authority, May 2014.
 "Caltrain Electrification Program: Environmental Assessment/ Final Environmental Impact Report, Volume 1," Peninsula Corridor Joint Powers Board, July 2008.
 "AC Transit 2010 Environmental Sustainability Report", Environmental Science Associates, March 2012.
 M. Mellera, A. Fritzler, and D. Sheeter, "Fiscal Year 2013 Departmental Climate Action Plan," San Francisco Municipal Transportation Agency, March 2014.
 "California: 2010 Census of Population and Housing, Summary Population and Housing Characteristics," U.S. Census Bureau, CPH- 1-6, December 2012.