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New Comprehensive Lifecycle Energy and Emissions Inventory Includes Non-Operational Components; Large Aircraft Can Perform Better than Light Rail
9 June 2009
A new comprehensive lifecycle energy, greenhouse gas emissions, and selected criteria air pollutant emissions inventory by researchers at the University of California, Berkeley that includes vehicles, infrastructure, fuel production, and supply chains found that find that total life-cycle energy inputs and greenhouse gas emissions contribute an additional 63% for onroad, 155% for rail, and 31% for air systems over vehicle tailpipe operation.
Inventorying criteria air pollutants showed that vehicle non-operational components often dominate total emissions. Life-cycle criteria air pollutant emissions are between 1.1 and 800 times larger than vehicle operation. Ranges in passenger occupancy can easily change the relative performance of modes, with large aircraft performing better than light rail in some of the areas investigated. The study was published 8 June in the open access IOP journal Environmental Research Letters.
In order to effectively mitigate environmental impacts from transportation modes, life-cycle environmental performance should be considered including both the direct and indirect processes and services required to operate the vehicle. This includes raw materials extraction, manufacturing, construction, operation, maintenance, and end of life of vehicles, infrastructure, and fuels. Decisions should not be made based on partial data acting as indicators for whole system performance.—Chester and Horvath (2009)
Mikhail Chester and Arpad Horvath inventoried on-road, rail, and air travel to determine energy consumption, greenhouse gas (GHG) emissions, and criteria air pollutant (CAP) emissions (excluding PM, lead, and ozone due to lack of data). The onroad systems include three automobiles—(2005 Toyota Camry), SUV (2005 Chevrolet Trailblazer), and pickup (2005 Ford F-150) to represent the range in the US automobile fleet and critical performance—and two urban buses with off-peak and peak passenger loadings.
83% of rail passenger kilometers are performed by metropolitan systems (with Amtrak serving the remaining). The researchers chose heavy rail electric metro, heavy rail diesel commuter transit, and light rail transit (LRT) to capture the gamut of physical size, fuel input, and service niche. Metro and commuter rail were modeled after the San Francisco Bay Area’s (SFBA) Bay Area Rapid Transit and Caltrain while the LRT modes are modeled after San Francisco’s (SF) Muni Metro and the Boston Green Line.
They evaluated small (Embraer 145), midsize (Boeing 737) and large (Boeing 747) aircraft to represent the range of impacts from aircraft sizes, passenger occupancy, and short to long haul segment performance.
US average data was used for all onroad and air mode components; particular geographic operating conditions was not captured. For each component in the mode’s life cycle, they calculated environmental performance and then normalized it per passenger-kilometer-traveled (PKT).
In the paper, the team reported the performance for modal average occupancy per-PKT.
Samples of the findings include:
- Off-peak urban diesel buses has the largest energy consumption and GHG emissions per PKT, followed by the three light-duty vehicles. Peak urban diesel buses showed the best overall energy consumption and GHG emissions per PKT.
- Of the non-road modes (rail and air), light aircraft showed the worst performance per PKT.
- While in terms of fuel consumption large aircraft exceed the energy consumption of the rail modes, when all elements are factored in, that total consumption in MJ/PKT is lower than that of SF Muni light rail.
- In terms of GHG emissions, large aircraft on a total g CO2e/PKT basis outperforms Boston light rail (the Green Line).
- In terms of sulfur dioxide emissions, Boston light rail was by far the worst performer, followed by SF Muni.
- For NOx, off-peak urban diesels were the worst performer, followed by light-duty vehicles and commuter rail.
- For CO, the pickup truck was the worst performer, followed by the off-peak bus.
In general, they found that the dominant contributions to energy consumption and GHG emissions for onroad and air modes are from operational components, suggesting that technological advancements to improve fuel economy and switches to lower fossil carbon fuels are the most effective for improving environmental performance.
However, they found that rail’s energy consumption and GHG emissions are more strongly influenced by non-operational components than onroad and air and concluded that while energy efficiency improvements are still warranted coupled with lower fossil carbon fuels in electricity generation, reductions in station construction energy use and infrastructure operation could have notable effects.
Reduction in concrete use or switching to lower energy input and GHG-intensity materials would improve infrastructure construction performance while reduced electricity consumption and cleaner fuels for electricity generation would improve infrastructure operation for rail, they noted. Utilizing higher percentages of electricity from hydro and other renewable sources for rail operations could result in significant GHG reductions over fossil-based inputs such as coal.
This study creates a framework for comprehensive environmental inventorying of several modes and future assessment of non-conventional fuels and vehicles can follow this methodology in creating technology-specific results.
Future work should also focus on environmental effects not quantified herein, such as the use of water, generation of waste water, and toxic emissions. Detailed assessments of the end-of-life fate of vehicles, motor oil and infrastructure should also be factored into decisions. Through the use of life-cycle environmental assessments, energy and emission reduction decision-making can benefit from the identified interdependencies among processes, services, and products. The use of comprehensive strategies that acknowledge these connections are likely to have a greater impact than strategies that target individual components.—Chester and Horvath
Mikhail V Chester and Arpad Horvath (2009) Environmental assessment of passenger transportation should include infrastructure and supply chains. Environ. Res. Lett. 4 024008 doi: 10.1088/1748-9326/4/2/024008
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