Emissions Calculators for Public Transit

Science Helps Managers Assess Life-Cycle Emissions

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Dr. Mikhail Chester is assistant professor of Civil, Environmental, and Sustainable Engineering at Arizona State University and co-director of the university's Sustainable Infrastructure Systems laboratory.

Posted: Wednesday, May 9, 2012 5:00 pm

Take a bus that runs on compressed natural gas and compare it to a light rail car. Which one is more environmentally friendly?

It depends. The light rail car has the potential to produce less air pollution because it runs on electricity. But if the source of the electricity is derived from coal, then its carbon footprint is bigger than the bus.

One scientist hopes his research will help decision makers and policymakers make informed choices when it comes to reducing the environmental impact of new and existing public transportation.

“We haven’t yet developed a consistent framework for assessing the comprehensive environmental footprint of transportation systems that includes moving the vehicle as well as its underlying infrastructure,” said Dr. Mikhail Chester, an assistant professor of Civil, Environmental, and Sustainable Engineering at Arizona State University.

When measuring greenhouse gases and other pollutants, Chester uses the life-cycle assessment method, a “well-to-wheel” approach that starts with the extraction of raw materials used in manufacturing and factors in operations, maintenance, fuel or energy production, infrastructure such as stations, roads and tracks, and finally disposal.

California High Speed Rail

Investments in new public transit systems can be examined through the lens of life-cycle assessment. For the California High Speed Rail project, a proposed 800-mile train system nearing final approval, the calculations required creating a model for a system expected to be operational in years 2030 to 2050.

The data for the California High Speed Rail system was based on trains from German manufacturer Deutsche Bahn. The model looked at the emissions outcomes with conventional and renewable electricity consumption. Chester and Dr. Arpad Horvath, professor of Civil and Environmental Engineering at UC Berkeley, calculated the total energy used to construct the project, and the following air emissions regulated by the Clean Air Act:

• Carbon Dioxide (CO2),

• Carbon Dioxide equivalent (CO2e)

• Sulfur Dioxide (SO2)

• Nitrogen Dioxide (NO2)

• Volatile Organic Compounds (VOC)

• Particulate Matter (PM 2.5 and PM 10).

“The reason that we've chosen to include a broad suite of air emissions, and not just CO2, is because we want to help identify policies that simultaneously reduce greenhouse gases and human health impacts,” Chester said at the American Planning Association's recent national conference in Los Angeles.

Chester and Horvath compared the rail project to other forms of transportation, including a 35-MPG sedan, electric vehicles, and next-generation planes. The results, calculated per passenger per kilometer traveled, vary depending on how many people ride the California High Speed Rail. If the rail is widely utilized by passengers, the sooner the payback in investment is likely to come. A high adoption of a future rail system would likely lead to significant reductions in California transportation emissions by shifting passenger trips away from cars and planes.

While critics of the high-speed rail system believe the project is too expensive, Chester points out that “if we decide not to build high-speed rail, we must consider how automobiles and aircraft will meet our growing transportation needs.”

Emissions Calculators for Public Transit

Transportation emissions account for nearly 30 percent of greenhouse gas emissions in the U.S., according to the Federal Transportation Administration. Of that amount, public transit systems account for just one percent, but are seen as part of the strategy to reduce the carbon footprint of the larger transportation sector, including by the FTA and its Transit Investment in Greenhouse Gas and Energy Reduction (TIGGER) funding program.

For now, transit agencies, voluntarily report their emissions to inventories such as The Climate Registry. Methods to do so are outlined in Recommended Practice for Quantifying Greenhouse Gas Emissions from Transit, by the Climate Change Standards Working Group of the American Public Transportation Association (APTA).

But legislation could make such reporting mandatory. The California Air Resources Board currently does not have such a requirement in the pipeline, according to a spokesperson. However, the state climate change law SB 375 would likely direct more regional transportation funding towards public transit systems and will need a method to quantify the greenhouse gas savings, according to the report Current Practices in Greenhouse Gas Emissions Savings from Transit by the Transit Research Cooperative Program.

A greenhouse gas emissions calculator in APTA's Recommended Practice looks at net savings by factoring in displaced emissions from car trips not taken due to the offset by public transit. The New York MTA estimates that 10 pounds of carbon are prevented from being released for each of its passenger trips. The Los Angeles County Metropolitan Transportation Authority (Metro) estimated in 2009 that the agency emitted a total of 483,000 Mt of carbon dioxide equivalent, or CO2e, but this amount can be offset of a savings of 391,000 Mt.

Many emissions calculators geared for public transit tend to look at direct effects such as tailpipe emissions, which is just one part of a life-cycle assessment. Optional reporting can include emissions from fuel or energy, but usually does not include manufacturing, as one example.

The emissions are expected to be higher if the calculator factors in parts of the life cycle, notably indirect supply-chain components such as fuel processes, vehicle manufacturing and infrastructure, according to a report by the U.S. Department of Transportation. Chester has found the increase to be as much as 70 percent for automobiles, 40 percent for buses, 150 percent for light rail, and 120 percent for heavy rail, which he documented as part of his dissertation Life-cycle Environmental Inventory of Passenger Transportation in the United States. Still, he says life-cycle assessments of public transportation are resource intensive, and he does not expect the method to be the standard for transit agencies.

However, new laws and regulations, such as California’s Sustainable Communities and Climate Protection Act, are opening the door for better measurement tools for cities to evaluate the comprehensive environmental footprint of new transportation systems to help meet SB 375 goals.

“We're trying to develop better measures across California,” said Chester.

Los Angeles Metro Study

In six months, Chester plans to complete a study of the Los Angeles County Metropolitan Transportation Authority (Metro), comparing emissions from the Orange Line Bus Rapid Transit (running on Compressed Natural Gas) and the Gold Line light rail.

The Orange Line Bus Rapid Transit system covers a 14-mile stretch running east to west in the San Fernando Valley, and is currently being extended by four miles. The Gold Line, a 19-mile route that Metro plans to expand in the future, runs from Pasadena to downtown to East Los Angeles. Both lines are fairly new, having opened less than a decade ago.

The life-cycle assessment offers Metro an opportunity to contribute to a study where results will be publicly available, in addition to providing Metro a different perspective of its own greenhouse gas emissions.

“I truly believe that a lot of new ideas can be used by Metro,” said Dr. Cris B. Liban, Metro’s Environmental Compliance and Services Department Manager. Nine years ago when Liban joined the agency, he said their approach to planning, design, construction, operations and maintenance was more traditional. A conventional way of looking at costs is purely financial, through the capital (construction) and operational budgets. The cost of a bag of concrete does not include an environmental assessment of where the limestone came from and its carbon footprint.

However, Liban is thinking a hybrid approach could be a possibility, but funding is always a factor. “Is there enough money in the project budget to do life-cycle costing,” said Liban. Of both the existing and new projects, it can be a fit for some projects, but not for others, he said.

Now more sustainable practices and policies have been institutionalized, he said. Specifically, as a result of recent Metro Board adopted environmental and sustainability policies, Metro has included more environmental requirements in the procurement documents for products and services.

But while environmental practices are part of Metro’s larger plan, the main priority of the agency is efficiently transporting passengers from point A to point B. This objective is more socioeconomic than environmental. Actions taken to green Metro need to be cost effective, meaning cheaper and better.

“Government agencies are trying to justify every cent of a tax dollar,” said Liban. Everything you do to a project involves some cost, he said. Yet results need to be tangible. Some examples of what Metro has implemented includes: efficiency lighting, recycling asphalt and concrete, reusing old structures of buildings instead of constructing from scratch, using reclaimed water instead of potable, and using drought-resistant plants for landscaping.

Quantifying and reporting emissions are something that Metro voluntarily does today, using APTA’s Recommended Practice. . The empirical data itself is not found online, but can be obtained through public records requests. Liban said that Metro’s quantified greenhouse gas emissions are those within their operational control, such as tailpipe emissions.

There are life-cycle components that are outside of Metro’s operational control, such as the source of where the energy is derived from. It includes the production of natural gas that their bus fleet uses and the electricity that the light rail runs on.

In the life-cycle assessment study's preliminary results, the Gold Line light rail is shown to produce more sulfur dioxide emissions than the bus–and even a sedan–per passenger mile traveled because the electricity it runs on is coal-based. To switch to electricity generated from renewable sources would make a significant difference, and the Los Angeles electricity mix is expected to reduce fossil energy sources in the future.

The study provides some different ways of looking at payback. Other preliminary results suggest that significantly more travelers need to shift from automobiles to the public transit systems in order to generate a net reduction in emissions. For the Gold line, 35 percent of trip takers would need to have been shifted from automobiles to guarantee that the new transit mode will provide an investment on return for all air emissions.

Ensuring that a large number of passengers shift from automobiles to the new transit lines can be aided by transit-oriented developments, providing walk and bike access, and more land-use planning, according to Chester.


Atlanta MARTA Study

Similarly, scientists and researchers at Georgia Tech’s School of Civil and Environmental Engineering calculated the footprint of their transit agency, Metropolitan Atlanta Rapid Transit Authority (MARTA). They also took a life-cycle assessment, factoring in the sources from which the energy (electricity, diesel, gasoline, natural gas, clean natural gas) was derived. MARTA's greenhouse gas emissions in 2008 were broken down as follows:

• 33% bus (diesel and Compressed Natural Gas)

• 11% paratransit (diesel)

• 28% heavy rail (electricity)

• 1.5% non-revenue vehicles (diesel and gasoline)

• 30% stationary sources (electricity and natural gas)

The stationary sources are infrastructure and buildings, and they produced nearly the same amount of greenhouse gases as the buses. Since the study, MARTA received a federal grant to install solar panels.

“If you have a lot of lighting, heating, cooling, then you'll have quite a bit of energy consumption [from buildings],” said Georgia Tech Professor Dr. Frank Southworth, who along with Dr. Michael Meyer and graduate student Brent Weigel prepared the Transit Greenhouse Gas Emissions Compendium. The study gathered the information about electricity usage from MARTA and also used data provided by the state. But in general, 51 percent of electricity in the U.S. is generated from coal, he said.

The life-cycle assessment included nearly all aspects, but not certain components such as the manufacturing stage or construction and maintenance of buildings, roads and tracks.

“We would like to look at more of the infrastructure, but there’s very little data on that. It’s very hard to get,” said Southworth. “What we're interested in is what a transit agency can control, such as lighting and heating a depot or an office building.”

Southworth said the ability to compare different transit agencies in a standardized life-cycle assessment of greenhouse gas emissions is an asset most agencies would welcome. Knowing which transit modes perform better than others can help decision makers choose the right modes for their particular location.

“To compare yourself with what other people are doing, you need a consistent metric,” he said.

Transit agencies have been among the most progressive when it comes to reducing greenhouse gases and keeping operational costs down, he said.

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