Fuel Tax versus Vehicle-Miles-Traveled Fee

The vehicle-miles-traveled (VMT) fee has been widely suggested as an alternative funding mechanism to the current state of practice, the fuel tax per gallon. The VMT fee has drawn researchers' and policy makers' attention, particularly regarding its equity performance in various social groups. With the introduction of the concept of vulnerable households, and with the use of socioeconomic-, geographic-, and vehicle-specific attributes from the 2009 National Household Travel Survey, the social groups in the United States that were most likely to be affected under each funding mechanism were identified through the estimation of three-stage least squares models at the national level. The results showed that households located in states with lower fuel taxation operated vehicles of lower fuel efficiency and thus contributed a larger portion of revenues generated by the fuel tax. In contrast, households with higher fuel-efficiency vehicles or with a higher average income generated more trips annually and thus would pay higher VMT fees at the household level. The study also examined whether the identified vulnerable households at the national level were different at the state level. With the use of the state of Iowa as a case study, the results suggested that, despite some similarities in the characteristics of the vulnerable households at the two levels of analysis, the development of state-specific models was statistically supported.