Despite the proliferation of these

Despite the proliferation of these incentives programs, their efficacy in actually promoting adoption of hybrids is unclear. To address that question, this paper examines the significance and strength of government incentives in promoting adoption, how the impact of incentive policies compares to other significant socioeconomic factors, and the implications of those relationships for policymakers. As a primary methodology, cross-sectional time-series analysis of HEV registration statistics over time from US states was used to test the relationship between hybrid adoption and a variety of socioeconomic and policy variables. A comparison of hybrid adoption patterns over time to the US average for specific states that have changed incentive policies was also conducted, to examine whether the way in which an incentive is implemented affects its impact. As a primary data source, state hybrid vehicle registration data from 2001 to 2006, provided by RL Polk & Co.,2 was used to calculate hybrid market share (i.e. new hybrids as a percentage of all new vehicles for a certain time period) for each US state.