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Study: Reducing Future Transportation CO2 Emissions to Kyoto Protocol Levels Will Require Combination of Vehicle Technology and Smart Growth

Percent change in median CO2 by scenario relative to 2000. Stone et al. (2009) Click to enlarge.

A Georgia Tech City and Regional Planning study on climate change concludes that “smart growth” combined with the use of hybrid vehicle technology could reduce cities’ carbon dioxide (CO2) emissions significantly by 2050. The study’s findings also suggest that meeting the reduction targets established by the Kyoto Protocol (1990 levels or lower) cannot be attained through vehicle technology change alone.

The research, led by Associate Professor Brian Stone, shows that expected levels of CO2 emissions from cars and trucks in 2050 could be reduced back to close to 2000 levels if the full vehicle fleet was converted to hybrid electric vehicles—a greater reduction in CO2 emissions than achieved by two smart growth scenario modelled in the study. The research also found that a doubling of population density in large US cities by 2050 would have a greater impact on CO2 reductions than full hybridization of the vehicle fleet.

Although the CO2 emissions reductions found to accrue under the two smart growth scenarios were lower than that of fleet hybridization as a stand alone strategy, our findings suggest urban densification holds the potential to approach or even surpass the benefits of hybrid technologies if region-wide densities can be increased beyond the levels modeled herein.

Our results suggest that, all else being equal, a doubling of mean population density throughout the median metropolitan area would have the effect of reducing vehicle CO2 emissions by about 30% relative to the BAU scenario, while the full dissemination of conventional hybrid technology was found to reduce vehicle CO2 emissions by 18%.

—Stone et al. (2009)

Stone’s study looked at 11 major metropolitan regions (MSAs, Metropolitan Statistical Areas) in EPA Region V (the Midwest) over a 50-year period and assessed four different scenarios:

  • Business-as-Usual Development Scenario (BAU). The BAU scenario assumes future population and land use trends throughout the study region will be consistent with historical change.

  • HEV Fleet Scenario (HEV). This scenario assumes that 100% of the study region’s vehicle fleet will be HEVs by 2050—half of which will be grid plug-in HEVs—but that the fleet will otherwise remain unchanged from 2000 in terms of its relative composition of different vehicle size classes.

  • Smart-Growth Development Scenario 1 (SG1). This scenario assumes the total population of each MSA in 2050 is the same as under BAU (business-as-usual), but that new population added in each decade is reallocated away from rural to suburban and urban census tracts in response to the widespread adoption of growth management policies, such as urban growth boundaries (UGBs) and transit-oriented development.

  • Smart-Growth Development Scenario 2 (SG2). In the SG2 scenario, a larger percentage of new MSA population growth is reallocated from rural to suburban and urban census tracts. Starting in the base year of 2000, all new population growth per MSA is directed to urban and suburban tracts only, with 10% of this growth directed to urban tracts and the remaining 90% directed to suburban census tracts in 2010. The urban allocation then increases by 10 percentage points per decade, rising to 50% of new population growth by 2050. Relative to SG1, SG2 results in higher urban populations and greater mean densities per census tract, as well as a larger number of tracts with densities of 10,000 people per square mile and higher.

The core of the study’s approach is a vehicle activity modeling framework for associating future land use and demographic characteristics, under BAU, SG1, and SG2 scenarios, with household vehicle travel. Using a framework originally developed by researchers at the Oak Ridge National Laboratory (ORNL), the Georgia Tech team estimated VMT (vehicle miles travelled) in response to three census variables: median household income, vehicle ownership, and employment rate, plus the neighborhood type classification.

Even the full hybridization of the national vehicle fleet by 2050 would not meet the CO2 targets identified though the Kyoto Protocol. According to Stone’s work, meeting this goal in the transportation sector would require a combination of technological improvements and higher density land use patterns in cities.

The results of our analysis suggest that continued dissemination of hybrid-electric engine technology would significantly offset the growth in vehicle emissions above base year levels independent of land use change. Should the full hybridization of the light duty vehicle fleet take place by 2050, it would offset virtually all of the expected growth in CO2 emissions under the BAU scenario.

An important contrast between the technological and smart growth strategies considered, however, is the implications of each for a wider range of problems associated with urban growth and vehicle use, such as traffic congestion, disinvestment in transit, and low rates of physical activity, as well as the life-cycle energy and pollution associated with the manufacture and disposal of vehicles. In light of the well documented problems associated with vehicle ownership and use in cities, climate change management strategies employing approaches rooted in both land use and technology change hold the potential to achieve the greatest offsets in mobile source emissions while addressing a wider array of problems associated with the growth of the vehicle population. In addition, our findings suggest that CO2 emission reductions needed to meet the targets established by the Kyoto Protocol (1990 levels or lower) cannot be attained through technology change alone.

—Stone et al. (2009)

The eleven metropolitan regions that were studied include Madison, Wisconsin; Columbus, Ohio; Indianapolis, Indiana; Minneapolis-St. Paul, Minnesota; Cincinnati, Ohio; Grand Rapids, Michigan; Chicago, Illinois; Detroit, Michigan; and Dayton, Ohio. In addition to Stone, Dr. Tracey Holloway, Scot Spak, and Adam Mednick also authored the study.


  • Brian Stone Jr., Adam C. Mednick, Tracey Holloway, and Scott N. Spak (2009) Mobile Source CO2 Mitigation through Smart Growth Development and Vehicle Fleet Hybridization. Environ. Sci. Technol., Article ASAP • doi: 10.1021/es8021655 • Publication Date (Web): 11 February 2009



How silly,
the most optimistic scenario is a 'full hybridization of the vehicle fleet'. So we take the modestly advanced technology of 2004 and do that for the whole fleet by 2050.

Even the worst cars of today do far better than the best cars of 1960 (within the same weight class).

With BEV or PHEV it should be much better than their scenario. The relatively small volumes of fuel still needed could easily be made out of algae or BTL.
If it's not possible to do that by 2050, technological advance should almost stop today.

The Goracle


Even more silly is the notion that humans releasing CO2 causes Global Warming® (now rebranded Climate Change® so that whichever way Earth's temperatures go - cooling for the past eight years - the people who will be making the big $$$$ off of this can say that they are correct).

This is all about the $$$$$. "Research" grants and government control of people's lives (more power for politicians).

Stop wasting our precious resourced on this Global Warming®/Climate Change® scam and start focusing on cleaning up pollution.



It definitely seems like a bit of an odd study. Kyoto protocol targets were meant to be achieved by 2012 (when it expires). Shooting for Kyoto targets in 2050 would be utterly futile (if we're just getting back to Kyoto at that point - we'll have long before triggered the heavy duty atmospheric feedback mechanisms / crossed the tipping points and our ability to control the CO2 level in the atmosphere, by decreasing our output, will be long gone) - i.e. our goose will be cooked by then.

While I disagree with Goracle's opinion regarding Global Warming (I'll believe the majority of scientists on this as opposed to the very rich, powerful and vested interests of the Fossil Fuel Industries / Trade Groups and who they pay), I have to somewhat share his opinion on the study. The basis of the study seems like something not thought through very well before undertaking.


Utterly backwards and unproductive. Kyoto is already dead. And as each day passes it becomes ever more clear that the role of man-made CO2 in global climate is negligible to zero.

2050? In forty years automotive propulsion won't be anything like the EVs today.


I love these 2050 projections. Did they factor in that there will be at least 11,000,000,000 people on the planet by then. That's double the population of 1995. Does anyone have a clue how much energy it's going to take just to feed that many people.


@ JosephT:

After the big cull of 2012 there'll be half what we have today. Plenty food to go around. And really low housing prices.


How about compulsory telecommuting for all information workers (50% in every modern industrialized society) and food and everything else from within 50 miles from home?


and... i forgot... allow use of private means of transportation *ONLY* for vacations.

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