This paper compared performance of methods for combining model information estimated in one region and applied to another region to improve estimation results. The application is for models developed to estimate household-level automobile-specific CO2 emissions. The results indicated that automobile-specific CO2 emissions models can be transferred from one geographical region to another. The estimates of CO2 emissions can assist agencies such as policy makers, businesses, and transportation planners to track trends and identify opportunities to reduce CO2 emissions and increase efficiency of transportation systems to lessen their impact on global warming, climate change, and air quality standards.