The National Academies

NCHRP 20-24(70) [Completed]

Update the 2003 Report Reducing Greenhouse Gas Emissions from U.S. Transportation
[ NCHRP 20-24 (Administration of Highway and Transportation Agencies) ]

  Project Data
Funds: $200,000
NCHRP provided partial support for this update project.
Research Agency: Pew Center for Global Climate Change
Principal Investigator: Judi Greenwald
Effective Date: 9/14/2009
Completion Date: 9/13/2010
Comments: Report was published by the Pew Center.


The future of surface transportation will take place in a context of policies related to global climate change and energy security. The transportation sector’s contribution to greenhouse gas (GHG) emissions in the U.S. represents about one-third of the total.  The U.S. Government, Congress, many Governors, State Legislatures, cities and counties are working to develop strategies which can achieve the goal of reducing U.S. GHG emissions 80% below current levels by 2050.

 According to EPA, GHG emissions in 2006 from all on-road vehicles stood at 1.6 billion metric tons. Over the last several decades they have been steadily increasing. To achieve emission reduction goals, instead of seeing on-road vehicle emissions increase, steps first need to be taken to arrest their growth and then steps need to be taken to assure their decline. Legislation on both climate change and the future of the federal highway and transit programs are pending in Congress this year. Each of them has or is expected to outline responsibilities state and local governments will be expected to carry out to help reduce greenhouse gas emissions.

The approach AASHTO is pursuing to help achieve overall transportation sector GHG reductions includes four parts: 1) increase vehicle fuel efficiency; 2) shift to fuels and sources of power which produce lower GHG emissions or zero GHG emissions; 3) reduce the rate of growth in highway vehicle miles traveled (VMT); and 4) improve system efficiency.  As federal, state and local governments work to identify the combination of strategies that will enable us to meet GHG reduction goals, it is important to assess what we can realistically expect to achieve from the individual solutions being advocated.


A noteworthy attempt by a credible national organization to conduct a comprehensive analysis of what could be done through various GHG reduction strategies was the report by the Pew Center on Global Climate Change titled “Reducing Greenhouse Gas Emissions from U.S. Transportation,” published in May 2003.


Since 2003, many changes have taken place which clearly justifies an updated analysis.  The most prominent of these has been developments in automotive technologies which point to earlier and more rapid implementation of plug-in electric hybrid automotive technologies and hydrogen fueled vehicles. There have been six years of experience with alternative fuels such as corn ethanol and bio-diesel. The record high fuel prices experienced in 2007 and 2008 appear to have increased consumer preference for more fuel efficient vehicles and decreased the market for less fuel efficient vehicles. Highway vehicle miles traveled (VMT) which had been growing steadily in the 1980’s and 1990’s actually declined from 3 trillion 2007 to 2.9 trillion in early 2009. Once the economy recovers VMT growth is expected to resume but at a slower pace, perhaps at 1% per year rather than previous rates of 2% or more.


At AASHTO’s request the Pew Center on Global Climate Change agreed to undertake an update of that 2003 report, to examine the overall potential GHG reductions from U.S. transportation, and help clarify the level of reductions obtainable from each component of the sector: vehicles, fuels, distance traveled, and system efficiency.   The report, "Reducing Greenhouse Gas Emissions from U. S. Transportation," authored by David Green and Steven Plotkin and dated January 2011, was published by the Pew Center. 


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