President Barack Obama recently announced a new federal policy to raise the mandated average gas mileage of cars and trucks, as well as reduce greenhouse-gas emissions. By 2016, the fleet-fuel-efficiency standard for all passenger cars will be 39 mpg, and 30 mpg for light trucks and sport-utility vehicles. Photo: Ford Motor Co. Slick hybrids could become jobsite workhorses. The average of these two equals a passenger-car and light-truck fuel-efficiency standard of 35.5 mpg. So what does this mean for future pickup-truck buyers? It depends. What is still to be determined are the exact rules that will have to be followed