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Tracking High-Speed Rail’s Energy Use and Emissions

A new life-cyle assessment makes it easier to compare and contrast the different transport modes with high-speed rail


SPRING 2010 — When it comes to the environmental costs and benefits of high-speed rail (HSR) versus cars or planes, or even heavy rail, such as Amtrak, Californians assume that HSR is the clear winner.

But is it? The answer is, it depends.

It depends on the type of power used to make the electricity to send the new trains up and down 800 miles of tracks. It depends on the energy efficiency of the train put into service. It depends on which emissions are measured. It depends on how many passengers are on a train, in a car, or on a plane when totaling up energy expended or emissions released. And it depends on the emissions created by building a large, new infrastructure requiring vast amounts of environmentally-intensive material.

Arpad Horvath (above left), Associate Professor of Civil and Environmental Engineering, and Mikhail Chester (above right), an ITS post-doc researcher, have made it easier to compare and contrast the different transport modes with their development of a life-cycle analysis for high-speed rail. Their work, “Life-cycle assessment of high-speed rail: the case of California,” was published recently in Environmental Research Letters

“This is the first comprehensive life-cycle assessment for high-speed rail,” explained Chester. “With this information we can provide a more holistic approach to understanding our transportation options in terms of their comprehensive environmental impacts.”

HSR has been touted as an environmental solution to the increasing impact of transportation on emissions in California. The electorate passed a nearly $10-billion bond in 2008 to begin the process of constructing the 800-mile project. Earlier this year, the federal government awarded the state another $2.25-billion.

'If we build the HSR system in California, we need to make sure we build it and operate it with the lowest environmental footprint, and incentivize people to take the train over other transportation modes.'

But under current conditions—with the model of HSR trains proposed and its energy source, as well as the types of automobiles and airplanes now in existence—the ITS researchers found that high-speed rail has the potential to be the lowest energy consumer and greenhouse gas emitter only if it consistently travels at high occupancy or uses a low-emission electricity source such as wind, both of which will require appropriate planning and continued investment.

For example, according to their findings a car with five passengers is energy-equivalent to California’s planned HSR with 1011 passengers and heavy rail with 298 passengers over a period of decades. They also note that while one mode may perform better than another at their average occupancies, there are many ridership levels where this may not be the case: one mode may not be as environmentally friendly as another mode at average loading, or occupancy. This is particularly important for HSR which may travel at 25% loading at some times and 90% loading at others.

Mode by mode analysis

The researchers came to their conclusions by comparing the energy and emission intensities of each mode per passenger kilometer traveled, using both high and low occupancies on HSR, on heavy rail, in cars, and on airplanes to determine the range in performance and the potentials of each mode to compete with the others.

They examined each mode’s life cycle and compiled exhaustive inventories for each—including everything from herbicide spraying and roadway salting associated with automobile travel, to runway lighting and deicing fluid production for aircraft, and track maintenance and infrastructure liability insurance for rail.

“We included hundreds of life-cycle processes in the components of these systems, from the construction equipment—for example, emissions from bulldozers, dump trucks, excavators, and frontloaders—and we looked at the supply chain effects of producing the materials—the concrete and steel needed to construct hundreds of miles of track and stations,” explained Chester.

Then they computed HSR’s Return on Investment, or ROI, in terms of energy consumption and emissions of greenhouse gases and sulfur dioxide and compared it to existing modes, which do not require new infrastructure. Depending on occupancy levels in all modes, there are scenarios where HSR will or will not perform environmentally better than the other modes: with 75 percent occupancy, HSR’s energy ROI is recouped in eight years, its GHG emissions in six years. But at 25 percent occupancy its ROI is infinite. At mid-level occupancy HSR ROI is achieved at 28 years for energy and 71 years for GHG emissions.

“If we build the HSR system in California, we need to make sure we build it and operate it with the lowest environmental footprint, and incentivize people to take the train over other transportation modes,” said Horvath.

The CO2/SO2 tradeoff

So why doesn’t HSR perform better?

For one thing, building a huge new infrastructure that relies heavily on vast quantities of steel and concrete counts against it, say the researchers.

“Producing concrete, particularly its cementitious component, is a GHG-intensive process,” said Chester, and concrete will be required in vast quantities for the rail project, not only in the construction of retaining walls and aerial track segments, but also stations and smaller facilities.

“High-speed rail in general may reduce GHG emissions, but you could have a situation where you’re trading those reductions for increases in other emissions, like sulfur dioxide.”

In their calculations, the researchers factored in only modest stations—not the larger terminals and buildings that are being discussed in major cities like San Francisco, San Diego, and Los Angeles. Nor did they include the processes and materials required to build tunnels under cities or through communities that object to the presence of high-speed rail above ground.

“By identifying processes within the life cycle that are significant in HSR’s overall emissions, we can start thinking about reducing environmental burdens by designing out these culprits. By reducing traditional infrastructure concrete use, for example, or by replacing it with less GHG-intensive alternatives,” Chester suggested.

While HSR’s huge new infrastructure counts against it environmentally, the electricity required to run the trains—and how it is produced—also has major environmental costs. Under the current electricity mix, high-speed rail will emit much larger amounts of sulfur dioxide than other modes because it will be fueled by California electricity, which is produced in part from fossil natural gas and coal. The other modes use lower-sulfur fuels and have emissions-control devices. In fact, the researchers noted that the ROI on sulfur dioxide emissions will never be achieved for HSR no matter how full its trains are packed.

“If we invest this money in HSR with a goal of reducing GHG emissions, then we should also consider purchasing high-priced but cleaner electricity or installing advanced sulfur controls at power plants,” says Chester. Sulfur dioxide emissions have ecological and  human health impacts that result in secondary particulate formation that can affect respiratory and  cardiovascular function. Those emissions also add to acidification of the environment.

“While GHGs are certainly important, we also want people to think of emissions affecting direct human as well as ecological health,” he added. “High-speed rail in general may reduce GHG emissions, but you could have a situation where you’re trading those reductions for increases in other emissions, like sulfur dioxide.”

Chester and Horvath suggest that while the California HSR system is still on the drawing board, planners might consider developing an alternative energy implementation plan, such as integration of a solar or wind infrastructure along the train corridor to lessen its environmental impacts.

The important thing is to be thinking about this now. “We need to be smart about this massive investment. We cannot rely on ‘becoming lucky’ after we spend dozens of billions of dollars,” says Horvath. 

Weighing other considerations

As for Horvath and Chester, now that the first high-speed rail life-cycle assessment is complete, they plan to refine it, and then examine more closely how shorter trips, say, from Fresno to Merced with particular operating characteristics, will compare environmentally to competition from automobiles and aircraft. This will give a more complete picture of how HSR will compare environmentally with particular train configurations and ridership.

“What we’ve done is establish a baseline: Here’s what California’s HSR looks like without much change in technology, using trains that have been around for some time,” explains Chester. “The next step might be to ask questions about possible changes in the design, as well as energy and environmental-intensiveness of system components. What if different train designs were implemented? Or cleaner electricity? What if a far greater number of cars on the road were hybrids? How does the next generation of aircraft change the picture?”

In other words, how might the environmental scorecard change?

Chester and Horvath acknowledge that we don’t make decisions purely on an environmental basis.

“Even if HSR is ‘dirtier’ in some environmental aspects than other modes, you may still choose to build it for several reasons,” says Chester. “These include transportation capacity constraints with the current infrastructure and the need to connect a growing number of cities, preferably avoiding developmental issues that have been identified with uncontrolled automobile growth.”

Adds Horvath,  “A well-functioning train system also has national security dimensions, may save passengers time in getting around California, and – let us not forget – may be more comfortable than other transportation modes. As a typical passenger, if the costs are similar enough, I’d always rather take the train than drive or fly.”

But a little more information never hurts. Especially when it comes to constructing the largest, new infrastructure in more than half a century in California.

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