A new analysis gives Californians good reason to be optimistic about the green credentials of the state’s proposed high-speed rail project, due to begin construction in 2013 thanks to funding recently approved by state legislators.

Arpad Horvath at the University of California, Berkeley, and Mikhail Chester at Arizona State University compared the future sustainability of California high-speed rail with that of competing modes of transportation, namely automobile and air travel. They determined that, in terms of energy consumption and greenhouse gas emissions, a mature high-speed rail system wins out when it deploys state-of-the-art trains powered by greener electricity. This was true even after accounting for the emergence of more fuel-efficient airplanes and automobiles.

The study, published today (Thursday, July 26) in the journal Environmental Research Letters, comes three weeks after lawmakers authorized $4.7 billion in state funds, which freed up an additional $3.3 billion in federal funds, for the high-speed rail project. The system promises to link Sacramento, San Francisco, Los Angeles and San Diego with trains traveling at a top speed of 220 mph.

The bill, signed into law by Gov. Jerry Brown last week, allows initial construction on the 768-mile rail system to begin next year.

“We’re showing that if this high-speed rail system is deployed, it is likely that California will reduce its transportation environmental footprint,” said Chester, who began this work as a UC Berkeley post-doctoral researcher. But to reap those environmental benefits, the state will have to wait until the system becomes fully operational, which could take an estimated 20-30 years after groundbreaking.

“What had been missing from the public debate is this long-term planning horizon,” said Horvath, UC Berkeley professor of civil and environmental engineering. “Comparable high-speed rail systems in Europe and Japan have been in place for 30-50 years. Why would we expect California’s system to provide a return on investment in a short period of time? I would compare where we are now to circa 1950, around the start of commercial air travel. Did anybody know then how many passengers LAX or SFO would eventually see in a year? Air travel has since grown into a massive industry.”

To assess sustainability, the researchers conducted an exhaustive life-cycle assessment that inventories the full range of environmental effects associated with each mode of transportation. Included in the analysis are the cradle-to-grave environmental costs associated with extracting, manufacturing and distributing the materials — such as concrete, steel and asphalt — needed to build and maintain the vehicles, freeways, tracks, stations and other integral components of the travel systems.

The researchers considered different scenarios, such as varying levels of ridership and renewable energy use, when calculating emissions of greenhouse gases and conventional air pollutants, acidification and impacts on human respiratory health.

Assuming that the electricity needed to operate the high-speed rail system comes from renewable sources, a goal set forth by the California High-Speed Rail Authority, the bigger impact of the project comes from infrastructure and supply chain processes. For instance, approximately 67 percent of infrastructure emissions attributed to high-speed rail are the result of cement production for concrete used in construction.

“If the high-speed rail project uses low-CO2 concrete, it could reduce the infrastructure’s environmental footprint by 15 percent,” said Chester, now an assistant professor at Arizona State University with joint appointments there at the School of Sustainable Engineering and the Built Environment, and the School of Sustainability.

The new study updates a 2010 analysis by Chester and Horvath with newer, more realistic system descriptions, data and projections, including forecasts for cleaner electricity.

One of the differences in the new analysis is the allowance for smaller, more energy-efficient trains, such as the InterCityExpress (ICE) high-speed trains already in use in Germany, that can be deployed based upon passenger demand. Instead of running a 1,200-passenger train at half capacity, for instance, the system could run smaller, more energy-efficient, 400-passenger trains during non-peak travel times.

When calculating the future energy consumption of cars, the researchers used the federal fuel economy standards goal of 35 mpg by 2020. The researchers also ran scenarios in which cars average 54.5 mpg by 2025, a standard proposed by the U.S. Environmental Protection Agency and the National Highway Traffic Safety Administration.

The researchers also accounted for next-generation aircraft that are expected to enter production within the next two decades. Such planes offer up to 20 percent in fuel consumption savings.

The findings indicate that when the proposed high-speed train is occupied by 80-180 passengers on average over its lifetime, it would result in as many greenhouse gas emissions on a per passenger-kilometer-traveled basis as a 35 mpg sedan carrying 2.2 people. The greenhouse gas emission-equivalent for a typical airplane carrying 116 passengers would be a train carrying 130-280 passengers.

“There are tradeoffs,” said Chester. “Depending on ridership, sometimes high-speed rail is better with greenhouse gas emissions and beats out cars and planes. For respiratory impacts, cars are typically the worst offenders, followed by high-speed rail and then airplanes. Overall, what we’re showing is that the trains are looking pretty good.”

Horvath pointed out that he and Chester matched existing state-of-the-art trains against cars and planes that are still emerging. If more energy-efficient rail technology emerges, he said, the environmental benefits would be even greater.

“It’s not clear what technologies will be available for high-speed rail in the future,” Horvath said. “We considered the best available technologies now, but there is nothing to say that it will be the best 10, 15 or 20 years from now. I’d be very surprised if best practices weren’t improved upon by then.”

Chester added that while their analysis shows environmental benefits to high-speed rail, “this is not the answer to the state’s greenhouse gas goals. This is a tiny piece of the puzzle.”

The researchers say that ultimately, planners and policy makers need to consider various factors beyond environmental impacts in developing California’s high-speed rail system. Changes in travel time, productivity, congestion, safety and urban development opportunities are just some of the deciding factors noted by the authors.

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