Greenhouse Gas Report 2005 - 2010

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  • Greenhouse Gas Report 2005 - 2010

  • Does bus transit have a positive effect on the community's overall net vehicle air emission levels?

    That is what the Orange County Transportation Authority (OCTA) has been studying for years. While the majority of our Greenhouse Gas (GHG) emission studies focus on the level of emissions our fleet generates during day-to-day operations, we are also measuring the impact bus transit has on reducing Orange County's overall GHG emission levels. We are looking at the effect of OCTA's public transportation when drivers shift from private vehicles to public transit and the corresponding reduction of congestion on our streets and freeways. It is these direct and indirect factors which play a role in the complex global GHG emissions equation.

    For guidance on understanding GHG emissions from our bus transit operations, OCTA has turned to the American Public Transportation Association (APTA) which has set standards for Quantifying Greenhouse Gas Emissions from Transit. These standardized methodologies aid in calculating “displaced emissions” when people shift from cars to bus and rail. The goal was to measure the net reduction in vehicle emissions from the business offerings of OCTA's public transportation.

    APTA's methodologies behind displaced emissions

    Shifting from cars to buses This category measures the displaced emissions associated from private vehicle drivers migrating to bus transit. On average, transit vehicles have much less carbon based exhaust than a private vehicle, often using fuels which result in lower emissions such as Compressed Natural Gas (CNG) and Liquefied Natural Gas (LNG). By displacing private vehicle travel with bus transit, a reduction in GHG emissions is expected.

    Congestion relief This category measures the emissions displaced when fewer cars are on the road, idling in traffic, and burning fuel. With fewer cars on the road, there is less congestion on the streets and freeways and lower GHG emissions as a result.

    Understanding the numbers

    When comparing the difference in net tailpipe emissions between 2005 and 2010, there are two key factors to consider. They include:

    • A decrease in passenger boardings from 6.7 million in 2005 to 5.1 million in 2010.
    • Advancements in clean fuel vehicles (both public and private) which have helped reduce total emissions.

    In conclusion, the total GHG emissions from OCTA's operations in the two years sampled show resulting data which is net-positive, -105,719 MT CO2 e in 2005 and -60,175 MT CO2 e in 2010 (See chart, upper right.). In Orange County, along with other communities which offer similar services, public transportation directly results in a significant reduction in GHG emissions by offering residents public transportation options and reducing privately owned vehicle traffic.

    GHG Chart Vertical


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