Date of Award

Spring 2015

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Civil Engineering

First Advisor

Samuel Labi

Second Advisor

Kumares C. Sinha

Committee Chair

Samuel Labi

Committee Co-Chair

Kumares C. Sinha

Committee Member 1

Fred L. Mannering

Committee Member 2

Raymond J.G.M. Florax

Committee Member 3

Loring F. Nies


Across the United States, the sustainability of highway funding is at risk due to increasing need and uncertainty in the factors that drive revenue. Past studies on highway funding sustainability have identified that the root cause of changing highway revenue are the shifts in social demographics and economic characteristics. Unfortunately, from the revenue perspective (the focus of this dissertation), the ability of previous research to account for these factors has been rather limited in two ways; first, the inability to accurately assess current regional vehicle use (a typical prerequisite for statistical modeling of highway revenues) due to difficulties associated with collecting data for local roads; second, the inability to directly account for the spatial dependence and heterogeneity that inherently characterize vehicle use, vehicle ownership, and socioeconomic attributes. ^ In addressing these issues, this dissertation focuses on revenue uncertainty and investigates the socioeconomic factors that influence passenger vehicle use and ownership and, by extension, the revenue generated from this class of vehicles. Spatial econometric models were used to capture the complex spatial trends that characterize the relationship between the influential factors and vehicle use and ownership. The models were used to estimate the impact of long-term socioeconomic changes on highway revenue from passenger vehicles. ^ This dissertation developed a unified framework incorporating spatial econometric modeling of regional vehicle use and ownership. This dissertation showed that vehicle use and ownership exhibit spatial dependence and heterogeneity which is caused by the influence of neighboring regions and unobserved spatial factors. Therefore, the research accounted duly for spatial heterogeneity and dependence, resulting in a more accurate and unbiased estimation. Also, the research yielded results suggesting that vehicle use and ownership are a function of the characteristics of a region as well as it neighbors. ^ The unified framework includes a robust methodology to estimate the current vehicle miles traveled (VMT) for all roads within a geographic region. The methodological approach uses spatial interpolation to impute unknown road segment values, overcoming an issue that typically impairs the traditional link-specific approach for estimating VMT. ^ This dissertation determines that, in order for the current level of funding from state gas tax revenue to be sustainable, the gas tax would have to be annually increased between 2.59% to 3.41%, depending on the forecast socioeconomic conditions. This annual increase in gas tax would allow agencies to recoup the effective fuel tax losses due changing vehicle use and ownership, inflation, and increased fuel economies. Unlike revenue from fuel taxes, revenue from passenger vehicle VMT fees is not susceptible to changing vehicle fuel efficiencies. To ensure funding sustainability, an annual VMT fee increase between 1.66% to 2.48%, depending on the socioeconomic conditions, is required; this would account for fluctuations in vehicle use and counteract the impact of inflation. The dissertation also determined that, in the likely event that a state is unable to collect VMT fees from out-of-state drivers (vehicles registered outside of the state), the fees would need to be increased by 12% to ensure funding sustainability.