According to the American Public Transportation Association (APTA), the trips Americans made using public buses, trains and subways in 2013 were the highest number ever recorded, since it started to keep track of such numbers based on passenger data from nationwide transit systems. A large passenger gain was recorded in Seattle, Miami, Denver, San Diego and even in Houston. Considering the many environmental benefits of public transportation, this can be a very encouraging news. But not all public transportation were created equal. Subway systems and light rail systems will be used in the following analysis to show that whether public transport is green or not depending on its energy sources.
New York City Transit is one of the most expansive and busiest subway systems in the world, because of its 468 stations which are the most of any transit system and its 1.6 billion annual passengers. This public transport system prevents close to 17 million tons of greenhouse gases annually while emitting two million tons, which is one of the largest sources of greenhouse gas reduction in the U.S. More than 80 percent of the electricity New York uses is generated from natural gas, nuclear power, and hydroelectricity.
In comparison, about 60 percent of the electricity the RTD light rail system in Denver uses is generated from coal. In August 2009, Denver Post published an opinion article comparing carbon dioxide emission from a single rider using RTD with that from driving 2008 model cars, using analysis from Randal O’Toole of Cato Institute. The result was for every passenger mile (one rider going one mile), RTD emits 0.59 pounds of carbon dioxide, while the numbers for general passenger car like sedans and the Toyota Prius are 0.54 pounds and 0.26 pounds, respectively. This highlighted the energy sources for electricity generation matter a lot when concluding the public transport is green or not.
Five years passed since this Denver Post analysis, and although coal still accounts for approximately the same portion of energy sources for electricity generation back then and now, the share of natural gas in electricity generation decreased from over 30 percent to 20 percent and the share of wind power increased drastically. The ridership of RTD light-rail system plays an important role when comparing the greenhouse gas emission from riding with that from driving. According to the recent trends, the ridership in Denver bumped up and this should reduce its carbon dioxide level per passenger mile. These two positive changes should make the RTD greener per passenger mile, but considering the increase of full-efficiency in traditional cars and the advancement of hybrid or electric cars in the same period of time, it is inconclusive that RTD is greener today.
The example of New York and Denver above demonstrated the energy sources used in generating electricity determine how green the public transport is. The worst source of electricity is synthetic natural gas (SNG) from coal-to-gas conversion, as being used in China. The increasingly unbearable air pollution challenges both the physical and mental tolerance level of the public, and eventually was acknowledged as a crisis in the annual meeting of its National People’s Congress last week. One of the solution is to build SNG plants to convert the vast coal reserve into natural gas for generating electricity. The conversion process is so water-intensive that it makes shale gas looks green and produces more greenhouse gas than simply burning the coal. Electricity from this source basically is impossible for any application to be green. Last week, Nanjing, a city in southern China, order 1,000 electric buses and taxis, in preparation for air quality improvement program in which it is one of the pilot cities. Knowing the direction of the development of electricity generation in China, this news is a lot less joyful than it could be.
Opinion by Tina Zhang