Highway Usage, Needs and Pollution as a Function of City Size and Population Density

Abstract. Using the data for 1990 urbanized areas from the 1972 Highway Needs Study, the effects of city size and population density on per capita vehicle use, miles of road, highway needs and “optimal”highway investment needs were investigated. The regressions showed that the miles of road per capita decrease with city population and population density. The vehicle miles of travel were found to increase with the land area of a city and its population. Although travel, and hence pollution increases in total as a city becomes more spread out, the suburban sprawl lowers the concentration of automotive pollutants in the atmosphere. Highway needs per capita decrease with population density, but increase with city size. Similar results are obtained when an approximation to optimal investment is used as the dependent variable.