Life-cycle assessment of transit

Introduction

Life-cycle assessment (LCA) is a technique to assess environmental impacts associated with all the stages of a product's life. 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 use 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

While it is difficult to assess LCA for transportation, a recent study on Los Angeles' transit systems show that when infrastructure, vehicle production, and energy production are taken into account, the environmental footprints of different transit modes increase significantly (Chester, 2013). 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 LA Metro expects to last 15 years, are manufactured in Hungary, assembled in Alabama, and then driven to LA. 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 LA to east LA 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; there will probably be increasing regional respiratory impacts in the near-term. 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 to begin 30-60 years after operations have begun.

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. 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.

Figure 3 - life-cycle results by passenger mile traveled for various environmental indicators. The Authors assume 1.7 people will be in the sedan, and that the near-term sedan gets 35 MPG, and the long-term sedan gets 54 MPG. Figure by Chester, et. al. (2013).

The authors show life-cycle emissions from door to door, looking at the impact that different ingress and egress options (on foot or bike, by bus, or by car) have on the trip. Figure by Chester, et. al. (2013).

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.

The figure shows the energy and emissions assessment of various travel modes. Calculations include not only operations, but also vehicle manufacturing, infrastructure construction and energy production. Graph by Chester and Horvath (2010).

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.

Additional Readings

Mikhail Chester. [http://iopscience.iop.org/1748-9326/8/1/015041/pdf/1748-9326_8_1_015041.pdf "Infrastructure and automobile shifts: positioning transit to reduce life-cycle environmental impacts for urban sustainability goals". (2013).

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.