Neighborhood Travel Emissions
Maps of carbon dioxide emissions from automobiles in three cities of differing geography and history reveal remarkable parallels. Maps of aggregate CO2 emissions generated on a per square mile basis in each city conform to conventional expectations regarding cities and pollution: high concentrations of people and industry generate high concentrations of pollutants.
While this is true in general terms, it masks the effect of urban form and land use on the emissions of individual households, which is often much less than that of rural or less dense equivalents. Maps of CO2 emissions generated per household in each of the three cities show a virtual inversion of the per square mile emissions values mapped in the first set of figures.
While the more densely populated areas of Chicago, Los Angeles, and San Francisco produce higher aggregate emissions than less densely populated outer suburbs and hinterlands, this relation of central city to periphery is inverted when the unit of measure is no longer gross emissions per unit land area, but rather gross emissions per household.
In the latter instance, the transportation efficiency of denser urban areas emerges clearly. On a per household basis, the lowest levels of emissions in all three regions are concentrated in the central cities, in those areas served by transit (particularly visible in the Chicago case), and along the commuter rails extending into the suburbs. Even in Los Angeles, it is the older, more densely inhabited zone extending from Santa Monica to downtown L.A., bordered on the south by Interstate 10, and on the north by the Santa Monica Mountains, that displays relatively high transportation efficiencies in comparison with the rest of the region.
These maps, based on fine-grained measurements of vehicle miles traveled in each city, offer visual confirmation of several decades' worth of literature describing the influence of urban form and density on travel demand. They also supplement this cumulative knowledge with a visual representation of the disproportionate contribution of lower-density, sprawling urban areas to total greenhouse gas emissions.