In 2001, the NRC released Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards. High oil prices and recent legislation mandating a further increase in the CAFE standards have renewed interest in the current and expected technical potential for automobile fuel efficiency. Accordingly, the National Highway Traffic Safety Administration (NHTSA) requested the NRC to provide an objective and independent update of the 2001 study and add an assessment of technologies that have emerged since that time. This report presents an interim assessment of technologies to be analyzed in the study and of the computational models that will be used in that analysis. Estimated fuel-economy benefits presented in this report reflect those from existing literature and presentations to the study committee. A final report is scheduled for late spring 2008.