The phenomenon wherein the modal share of cars and the total distance traveled by car begin to decrease—referred to as “peak car”—has been occurring in the Keihanshin Metropolitan Area in western Japan. It is believed that age, sex, cohort, and the built environment, affect patterns of car use. This research aims to quantify the characteristics of car use and estimate the modal share of cars in 2020, taking the above-mentioned factors into account. Data from person trip surveys conducted every 10 years from 1990 to 2010 are used to analyze the longitudinal changes in car use characteristics. The results indicate that characteristics of car use are indeed related to age, sex, cohort, and built environment, and the modal share of cars will decrease in the central regions of the Keihanshin Metropolitan Area by 2020 while increasing on the edges of the metropolitan area.