Wall Street Journal: Since Henry Ford began mass production of the Model T nearly a century ago, car-loving Americans have gulped ever-increasing volumes of gasoline. A growing number of industry players believe that era is over. Among those who say U.S. consumption of gasoline has peaked are executives at the world’s biggest publicly traded oil company, Exxon Mobil Corp., as well as many private analysts and government energy forecasters. The reasons include changes in the way Americans live and …