Impact of Public Transportation Market Share and other Transportation and Environmental Policy Variables on Sustainable Transportation

Policies that encourage reduced travel, such as traveling shorter distances, and increased use of more efficient transportation modes, such as public transportation and high-occupancy private automobiles, are often considered one of several possible tools aimed at improving the sustainability of transportation. This study develops a statistical model that provides an important step towards quantifying the possible benefits that could be derived from such policies in terms of potential reductions in greenhouse gas (GHG) emissions. The contributions of this study are fourfold. First, an aggregate model of urban passenger travel related CO₂ emissions in US urbanized areas that includes a rich set of explanatory variables is developed. Second, in doing so, the roles of policies aimed at improving the environment or could enhance the attitudes of travelers towards making environmentally favorable choices is captured through the use of a proxy variable. Third, the possible presence of selectivity bias resulting from the hypothesized effects of such environment enhancing policies is accounted for in the model estimation. Fourth, as a result, an improved quantification of the explanatory effects of transportation demand and supply, population density, and policy variables is arrived at.