Role of Transit in a Low-GHG California

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Reducing the impact of green house gas (GHG) emission on the environment has become a national priority. The State of California had made it a goal to set targets for reducing GHG emission through enacting Senate Bill 375. About half of all GHG emissions in the U.S. come from transportation,and about 85% of those are from the surface transportation sector.[1] Transit agencies can play a significant role in slowing the growth of GHG emissions as part of a carbon reduction regime stressing improving connections between land use and transportation and increasing the availability and quality of public transport. The APTA states that public transportation can reduce CO2 emissions by 37 metric tons annually by reducing the growth in vehicle miles, easing congestion and supporting more efficient land use. This will be needed to meet 2050 federal standards even with improved fuel economy from revised CAFE standards as private vehicle use represents over half a typical household's carbon footprint.[2] These efforts can be combined with support for bicycling, walking, and traffic and parking management, as well as higher density development that supports transit use.

Innovative Approaches

A TCRP report on international efforts to address climate change suggest that U.S. transit providers can benefit from some of the approaches taken in European cities for reducing automobile dependence.[3] Examples include implementing quality bus corridors (QBCs) which provide shorter journeys and more consistent service through dedicated bus-only lanes and traffic signal prioritization, and coordinated feeder routes. Munich uses a mobility management system to provide new residents with information about transit options, while Frieberg, Germany adopted a regional transit pass that can be used on multiple systems to make using transit easier and increase ridership. It also provides facilities for bicycle storage and rental at its central station, and offers free and discounted transit passes for those who subscribe to a car sharing program. The public transport authority for Milan, Italy has plans to improve parking outside the city center to encourage use of public transit, as well as supporting bicycle and car sharing programs, and improving pedestrian areas. The city's Ecopass program charges vehicles entering the center of town according to the pollution they generate with the objective of reducing automobile use so that public transit can provide better service. The fees collected are invested in sustainable transport. Metro Bilbao in Spain offers extremely frequent low-fare service on its two lines which is "fine-tuned" to match demand. Several continental systems are moving toward more energy efficient transit vehicles, purchasing lighter weight aluminum cars, adding regenerative braking and on-board capacitors for energy storage, monitoring energy consumption on cars, increasing their use of biofuels and hybrid-electric vehicles, and developing more efficient operating patterns. Despite historical differences between government frameworks and the role of the automobile between European and American cities, the authors of the report believe that transit can be can be a successful part of a climate change strategy.

A number of US cities have already adopted innovative approaches including use of electric and diesel-electric hybrid vehicles, regenerative braking and energy storage, and use of alternative fuels including biofuel, natural gas, and hydrogen cell technology.[4] The APTA has called for an investment of 1.6% of GDG to increase transit use up to 10% annually to put transit's market share on par with the European Union by 2030. It projects a net savings from the plan of 141.9 million metric tons of carbon emissions per year.[5]

Alternative Fuels

Although diesel engines used by many transit vehicles are much less polluting than previously, additional emissions reductions can be achieved by the use of biodiesel fuel, made from soy beans and other organic material, as outlined in a recent TRCP report.[6] Adding biodiesel to regular petroleum diesel can reduce emissions with only a small loss of fuel economy but also make cold weather operations more difficult, necessitating fuel management strategies. A blend of 20% biodiesel and 80% regular petroleum diesel is known as B20 and is easy to use in regular diesel engines. According to this study, concentrations of B20 or less can reduce total unburned hydrocarbons (HC) by 20%, both carbon monoxide (CO) and particulate matter (PM) by 12% each, and help reduce atmospheric carbon. The effect on NOx emissions is less clear. Higher concentrations, including pure biodiesel B100, can be incompatible with some engine materials and can gel at low temperatures, but there are ways to mitigate these effects. One main advantage of biodiesel is that the CO2 is actually consumed in the process of growing the crops to make biodiesel. A Department of Energy study showed that substituting B100 for petroleum diesel reduces life-cycle CO2 emissions by 78%, compared to 16% for B20.

Further Reading

American Public Transportation Association, "Public Transportation Reduces Greenhouse Gases and Conserves Energy."

This brochure outlines the environmental and energy saving benefits of public transportation and discusses how increased investment in transit is beneficial to future climate change and energy legislation.

American Public Transportation Association, "Transit on the Cutting Edge of Clean Technology," September 2012.

This white paper reviews the progress transit agencies have made investing in innovative clean technologies and fuels, including electric and hybrid vehicles, electric storage, biofuels, natural gas, and hydrogen fuel cells.

American Public Transit Association, "Changing the Way America Moves: Creating a More Robust Economy, a Smaller Carbon Footprint, and Energy Independence," Spring 2009.

This paper argues for a national commitment to invest in public transit to reduce congestion, save fuel and improve the environment. It documents the long-term benefits in reduced carbon emission from a 5-10% increase in annual ridership through 2030 and 2050.

Center for Neighborhood Technologies, "The Route to Carbon and Energy Savings: Transit Efficiency in 2030 and 2050," November 2010.

This report identifies 17 high-priority strategies that transit agencies can take to reduce energy use and GHG emissions and estimates the potential impacts of those strategies in 2030 and 2050.

Science Applications International Corporation (SAIC), "Public Transportation’s Contribution To U.S. Greenhouse Gas Reduction", September 2007.

This report addresses current and potential C02 savings from public transportation compared to non-public transportation commuting what can households do to save more. It also discusses favorable land use, environmental and social benefits from public transportation.

Transit Cooperative Research Program, Research Results Digest 89, "Public Transportation's Role in Addressing Global Climate Change,", March 2009.

This TCRP digest prepared by the Eno Foundations summarizes the Spring 2008 mission performed under TCRP Project J-03, “International Transit Studies Program.” This digest includes transportation information on the organizations and facilities visited and their strategies to combat climate change through public transportation.

Transit Cooperative Research Program, Research Synthesis 72, "Use of Biodiesel in a Transit Fleet," 2007.

This report documents a full range of benefits offered by biodiesel and closely examines biodiesel implementation at two transit agencies as case studies, so that transit agencies can make informed decisions regarding its use.Topics covered by this study include engine manufacturer requirements and warranty considerations, maintenance implications, emissions testing results, cold weather operations, fuel specifications and procurement considerations, fuel storage, and delivery.


  1. APTA, "Public Transportation Reduces Greenhouse Gases and Conserves Energy." [APTA Brochure]
  2. APTA Brochure
  3. Transit Cooperative Research Program, Research Results Digest 89, March 2009.
  4. APTA, "Transit on Cutting Edge of Clean Technology," September, 2012.
  5. APTA, Changing the Way America Moves: Creating a More Robust Economy, a Smaller Carbon Footprint, and Energy Independence." Spring 2009.
  6. Transit Cooperative Research Program, Research Synthesis 72, 2007.