Urban population density may influence transportation demand, e.g., as expressed through average daily vehicle-kilometers traveled in private motor vehicles per capita. In turn, changes in transportation demand influence total passenger vehicle emissions to which populations are exposed. Population density can also influence the fraction of total emissions that are inhaled by the exposed urban population. Equations are presented that describe these relationships for an idealized representation of an urban area. Using analytic solutions to these equations, we investigate the effect of three changes in urban population and urban land area (infill, sprawl, and constant-density growth) on per capita inhalation intake of primary pollutants from passenger vehicles. For the system considered, the magnitude of these effects depends on density-emissions elasticity (ε e), a normalized derivative relating change in population density to change in vehicle emissions. For example, based on the idealized representation of the emissions-to-intake relationship presented herein, if urban population increases, then per capita intake is less with infill development than with constant-density growth if ε e is <-0.5, while for ε e >-0.5, the reverse is true.
Bibliographical noteFunding Information:
This work was supported in part by a Graduate Research Fellowship from the National Science Foundation, by a University of California Toxic Substance Research and Teaching Program fellowship, by a grant from the University of California Transportation Center, by Cooperative Agreement Number U50/CCU922409-01 from the US Centers for Disease Control and Prevention (CDC), and by the US EPA National Exposure Research Laboratory through Interagency Agreement No. DW-988-38190-01-0, with the Lawrence Berkeley National Laboratory operated for the US Department of Energy (DOE) under Contract No. DE-AC03-76SF00098. The contents of this paper are solely the responsibility of the authors and do not necessarily represent the official views of the CDC, EPA, or DOE. The authors thank Dr. John Holtzclaw for providing data on population density and daily per capita vehicle-kilometers traveled for traffic analysis zones in Chicago, San Francisco, and Los Angeles.
- Land-use planning
- Population density
- Smart growth
- Transportation planning