In addition to the blooming cherry blossoms in Washington, D.C., a flurry of climate-related goals and proposals have emerged from the White House and Congress with the overall ambition of reducing greenhouse gas emissions and reducing the carbon footprint of the federal government and transportation sector. When looking at these proposals, you may hear the phrases “tailpipe emissions,” or “life-cycle analysis” or “well-to-wheel.” What do they mean? Are they different? Does it really matter?
In looking at environmental and air quality standards and benchmarks, it is necessary to measure and quantify the emissions that are being regulated. The transportation sector is the primary focus of much of these proposals. Vehicle emissions can be divided into two general categories: air pollutants, which contribute to smog and haze, and greenhouse gases, such as carbon dioxide and methane. Both categories of emissions can be evaluated on a direct basis (i.e., tailpipe emissions standard) or with a life-cycle analysis (i.e., well-to-wheel basis).
Tailpipe emissions standards measure certain pollutants that are emitted from an internal combustion engine. This standard was first introduced in California in 1959 to control carbon monoxide and hydrocarbon emissions from gasoline engines.
Well-to-wheel emissions standards look at all the emissions and environmental impact related to fuel production, processing, distribution and use—not just from the tailpipe of a vehicle. In the case of gasoline, emissions produced while extracting the petroleum from the earth, refining it, transporting the fuel to gas stations and then the burning of the fuel in the vehicle would be included in the analysis.
Understanding the difference between tailpipe emissions standards and life-cycle analysis is important when comparing the environmental impact between a vehicle powered by an internal combustion engine or a zero-emission vehicle powered by electricity. If you made a comparison between the two cars and used a tailpipe emissions standard, a conventional vehicle with an internal combustion engine produces direct emissions though the tailpipe, as well as through evaporation from the car’s fuel system and during the fueling process. Conversely, an electric vehicle would produce zero direct emissions.
However, life-cycle or well-to-wheel analysis would include all emissions related to fuel production, processing, distribution and use. In the case of an electric vehicle, it would look at the power source generating the electricity (e.g., coal, natural gas, hydro, nuclear, solar, wind, etc.) and how it is extracted, processed and distributed for the use of electric generation. Thus, an electric vehicle that uses electricity generated by coal would have a very different emissions impact from an electric vehicle powered by electricity generated from solar or wind.
As policymakers look at the future of how the cars we drive are going to be powered, it is important to understand what standard is going to be used to compare the environmental impact of different fuels and vehicles. In looking at environmental policy, NACS believes science should be the foundation for transportation climate and environmental policies, and any effort to improve the transportation industryís greenhouse gas emissions requires an accurate accounting of the life-cycle carbon intensity associated with particular fuels and technologies.