Life-cycle assessment of transit
Life-cycle assessment (LCA) is a technique to assess environmental impacts associated with all the stages of a product or project's life - from cradle to grave. For transportation, this would include energy consumption and emissions for vehicle, infrastructure, and energy productions components, beginning with material extraction and processing all the way through operations and maintenance.
Public transportation systems are often part of strategies to reduce urban environmental impacts, which can be seen in the goals of California's SB 375. However, comprehensive energy and environmental impacts are rarely considered. While many transit agencies will often market their contributions to reductions in auto trips or carbon monoxide emissions, vehicles don't exist in isolation, but rather require a large and complex system to support their operations. A LCA approach is especially important for new mass transit systems that produce large upfront impacts for long-run beneﬁts, but to date, few studies examine the life-cycle costs and benefits of deploying transit.
LCA of Los Angeles' Orange and Gold Lines
Researchers at Arizona State University and the University of California at Los Angeles studied the Los Angeles Metro Gold Line light rail and Orange Line bus rapid transit, conducting a life-cycle assessment of energy use, greenhouse gas emissions, and other emissions from construction, operation, and maintenance of new transit lines and automobile infrastructure (Chester, 2013). Many environmental analyses focus only on one phase, such as construction only or operations only. Life-cycle assessment allows researchers and policymakers to fully evaluate global changes that result from the decision to build new transit, and the projected effect that decision has on automobile trips. The study looks at the Orange Line bus rapid transit (BRT) and the Gold Line light rail (LRT); the following summarizes the findings.
The Orange and Gold Lines
The Orange Line BRT is an 18-mile dedicated right-of-way running east–west through the San Fernando Valley. The Orange BRT buses, which Los Angeles Metro expects to last 15 years, are manufactured in Hungary, assembled in Alabama, and then driven to Los Angeles. The 17 miles of dedicated busway consists of roughly 13 miles of asphalt and 4 miles of concrete surface layers, and the initial construction of the right-of-way does not create significant environmental impacts; the payback for GHGs is almost immediate.
The Gold Line LRT consists of 19.7 miles running from downtown Los Angeles to East Los Angeles and Pasadena. There are currently 21 stations, and 2,300 parking spaces across nine stations. The Gold Line trains are manufactured in Italy and shipped by ocean vessel to LA. The trains consume approximately 10 kWh of electricity per vehicle mile traveled, which is important to consider since 39% of LADWP electricity is currently produced from coal. In the near-term, even when infrastructure, vehicle, and fuel impacts are included, the Los Angeles Orange and Gold lines will have lower per-passenger-mile energy use and greenhouse gas emissions compared to a new higher efficiency (54 mile per gallon) automobile. In the long-term, vehicle technology improvements and cleaner electricity will help reduce transit’s energy use and environmental impacts by 42-93%. Concrete is responsible for a significant portion of the Gold line’s greenhouse gas emissions from construction. Using low-CO2concrete or advanced emission control technologies in the future could reduce construction emissions and improve the payback time. Additionally, the heavy use of concrete for Gold line tracks results in signiﬁcant CO2, VOC, and PM2.5 releases during cement and concrete production. The study estimates payback under near-term conditions to occur 30-60 years after operations have begun.
In the long-term, vehicle technology improvements and cleaner electricity will help reduce transit’s energy use and environmental impacts by 42-93%. Concrete is responsible for a significant portion of the Gold line’s greenhouse gas emissions from construction. Using low-CO2 concrete or advanced emission control technologies in the future could reduce construction emissions and improve the payback time.
Comparisons with Cars
The study looks at auto trips that would have substituted the Gold and Orange lines, had they not existed. In the near-term, both the Orange BRT and Gold LRT lines can be expected to achieve lower energy and GHG impacts per PMT than emerging 35 mpg cars and even future 54 mpg cars. Vehicle operations constitute the majority of life-cycle effects, which are local; in contrast, vehicle manufacturing and energy production produce significant non-local environmental impacts. In the long-term, automobile fuel economy gains, reduced emission buses, and non-coal powered electricity will have the greatest impacts on passenger transportation energy use and GHG emissions in LA.
LCA of California's High Speed Rail
California is planning to spend $40 billion to build a high speed rail (HSR) system from San Diego to Sacramento. With increased concern for energy use and climate change, the HSR is often touted as less energy-intensive and GHG-emitting than cars, heavy rail, and aircraft. However, the calculations for energy consumption, greenhouse gas emissions, and other emissions typically only consider vehicle operations. Additionally, there is great uncertainty about future ridership levels. Taking ridership uncertainty and life-cycles into account yields drastically different estimates about the energy efficiency of different transportation modes. 
For example, light rail with 90 percent occupancy would compare favorably with just about any other mode if only the energy and emissions of operations were considered. However, building the infrastructure and producing the fuel would double the energy intensity of light rail. Furthermore, if occupancy assumptions were lowered to only 10 percent full, as opposed to 90 percent, then light rail becomes less environmentally beneficial than a gasoline sedan with a solo driver  Additionally, while carbon emissions could be lowered in the long run, sulfur dioxide emissions will remain a problem unless California's energy portfolio changes to include cleaner sources. 
Perhaps one of the most important conclusions drawn from LCA is investments in HSR or other transit modes do not automatically generate benefits. Utilization is a critical factor; the larger the shift the quicker the payback, which should be considered for time-specific environmental goals. While one transportation mode may outperform the others at their average occupancies, there are many ridership levels where this may not be the case.
- This study uses LA's Orange and Gold lines as a case study to calculate transit's near-term and long-term life-cycle impact assessments.
Mikhail Chester and Arpad Horvath. "Life-cycle assessment of high-speed rail: the case of California" (2010).
- The considerable investment in California high-speed rail has been debated for some time and now includes the energy and environmental tradeoffs. Most studies only consider vehicle operations, but this report also includes indirect effects from vehicle, infrastructure, and fuel components.
Mikhail Chester, Juan Matute, Paul Bunje, William Eisenstein, Stephanie Pincetl. Life-Cycle Assessment for Transportation Decision-making. Forthcoming from the California Energy Commission.
- Guidance for how California transit agencies can incorporate life-cycle assessment into existing planning, procurement, and construction processes.