Study: Energy-Efficient Urban Form

Here’s another study arguing how compact urban development is key to mitigating climate change gas emissions. Communities that are planned to be transit-oriented and friendly to bicycling and walking are the future for this country. Embrace it!


Reducing urban sprawl could play an important role in addressing climate change.

Julian D. Marshall
UNIVERSITY OF MINNESOTA
Published in Environmental Science & Technology

Improving city layouts and transportation networks could reduce carbon emissions more than replacing all gasoline with corn ethanol (1). Although much attention on mitigating climate change has focused on alternative fuels, vehicles, and electricity generation, better urban design represents an important yet undervalued opportunity. Fortunately, such decisions are well within the reach of local governments and leaders and can reduce long-term carbon emissions.

The impact of cities—and urban design—on the global climate is becoming increasingly important. In 2008, urbanites will outnumber rural dwellers globally for the first time in human history (2). China's population doubled between 1952 and 2003, but its urban population increased 7-fold; today, 170 Chinese cities have at least 1 million residents (3). The U.S. has 39 such cities (4). In coming decades, urban populations are expected to double while rural populations level off or decline.

Vehicle use is rising rapidly. From 1970 to 2005, U.S. total vehicle-kilometers increased 3× faster than the population (annual increases: 3.0% vs 1.0%) (5). Similar trends occurred in China (8.3% vs 1.7%, a 5-fold difference) and the world (4.3% vs 1.8%) during 1970@1990 (6). If current trends in total vehicle-kilometers continue, vehicle CO2 emissions may increase even if emissions per mile decline (7).

In an influential paper in Science, Socolow and Pacala (8) argue that climate stabilization during the next half century means reducing CO2 emissions by 175 GtC (33%) relative to a business-as-usual (BAU) scenario. They propose seven strategies, with each “stabilization wedge” representing emission reductions of 25 GtC during 2005@2054 (each wedge grows from no reduction in 2005 to 1 GtC per year [yr] reduction in 2054).

The race is now on to figure out ways to design and implement these wedges. Often neglected in the debate is the role of urban form (e.g., land-use patterns and the layout of transportation infrastructure) in meeting climate objectives. My estimates suggest that reducing urban sprawl in the U.S. alone could represent half or more of a stabilization wedge.

Impacts of urban form on transportation CO2

Compact urban form can cut on-road gasoline emissions, the largest segment (62%) of transportation CO2 in the U.S. The transportation sector is the largest emitter (33%) of CO2, outpacing the residential, industrial, and commercial sectors. (Electricity generation, when totaled for all sectors, accounts for 41% of CO2 emissions.) Records of automobile usage (Figure 1) show an inverse relationship between population density and per capita daily vehicle-kilometers traveled (VKT) (4, 9). Evidence suggests that VKT is causally related to population density and other urban form attributes, and therefore, sprawl reduction policies may curtail VKT (10@14). In denser urban areas, trip origins and destinations (e.g., home, work, shopping) are closer; driving disincentives (e.g., congestion, parking costs) are greater; and alternative modes of travel (e.g., walking, bicycling, mass transit) are more common (15).

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Note from BikePGH: this is the Pittsburgh Metropolitan Statistical Area, not just the city. If only the city were taken into account we would doubtless see our VKT decline

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