Fuel Options for Reducing Greenhouse Gas Emissions from Motor Vehicles

Pickrell, Don · 2003 · ROSA P / United States. Dept. of Transportation. Research and Special Programs Administration

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Summary

This 2003 report by the U.S. Department of Transportation assesses the potential of alternative fuels to reduce greenhouse gas (GHG) emissions from automobiles and light-duty trucks. The study evaluates substitutes for gasoline, including ethanol, compressed natural gas (CNG), liquid petroleum gas (LPG), diesel, biodiesel, electricity, and hydrogen, under specific assumptions regarding vehicle travel growth and fuel replacement rates. The analysis covers both near-term (10-year) and long-term (25-year) horizons, assuming that alternative fuels could replace 10% of projected gasoline use by 2010 and 25% by 2025. The report also examines the cost-effectiveness of these strategies and addresses secondary concerns such as infrastructure requirements, feedstock availability, and compliance with criteria pollutant standards. The methodology relies on full fuel cycle analysis, accounting for emissions from both vehicle operation ("tailpipe") and fuel production, distribution, and refining ("well-to-tank"). The study assumes internal combustion engines remain the dominant technology, though it also explores the impact of advanced technologies like direct-injection engines, hybrids, and fuel cells. Key assumptions include a moderate annual growth in vehicle miles traveled and a shift toward smaller light trucks. The analysis quantifies GHG reductions in total metric tons, allowing for comparison against economy-wide emission targets. The findings indicate that replacing gasoline with most alternative fuels yields modest GHG reductions. In the near term, replacing 10% of gasoline use with corn-based ethanol, diesel, biodiesel, or electricity reduces full fuel cycle GHG emissions by only 2–3%. CNG and LPG show negligible reductions (0–1%). Over the longer term, replacing 25% of gasoline use with petroleum diesel, biodiesel, or electricity could reduce emissions by 8–11%. However, cellulosic ethanol could achieve reductions exceeding 20% if commercialized. Advanced engine technologies, such as hybrids and fuel cells, offer significantly larger per-mile emission reductions (up to 87%) but face uncertain commercialization prospects. The report also notes that diesel substitution raises concerns regarding nitrogen oxide and particulate matter emissions, potentially conflicting with federal standards. The study concludes that promoting alternative fuels is a costly and inefficient strategy for reducing GHG emissions. High capital costs for vehicle manufacturing, fuel production, and infrastructure development make most alternatives unattractive from a cost-effectiveness standpoint. For instance, near-term cost-effectiveness analysis shows high costs per ton of GHG avoided for most fuels. Furthermore, widespread adoption requires substantial infrastructure investment and adequate feedstock supplies. While alternative fuels are not inherently more dangerous than gasoline, the transition involves significant logistical and economic challenges. The report suggests that innovations in engine technology may offer comparable or greater emission reduction potential than fuel substitution alone, though both face implementation hurdles.

Key finding

Replacing 10% of projected gasoline use with corn-based ethanol or petroleum diesel reduces full fuel cycle greenhouse gas emissions by only 2-3%, while replacing 25% of gasoline with cellulosic ethanol or electricity achieves reductions of 22% and 11% respectively.

Methodology

modeling

Provenance

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