Big automakers are acting way too cautious to meet the 2025 deadline to average 54.5 mpg, according to pioneering light-car designers. If that's the average, it means car fleets are going to need some models that get many more miles per gallon than that. And it isnít easy, said Oliver Kuttner, founder and CEO of Edison2, which developed a gasoline-engine car that can top 100 mpg and won $5 million in Progressive Insuranceís Automotive X Prize in 2010. Since then, Edison2 has developed an electric car rated at 245 mpg. "I do believe that the lowest-hanging fruit is to start to open your eyes to the possibility of changing systems," Kuttner said. He said mainstream automakers are in for a rude awakening. It takes at least five years and a whole new approach to design to accomplish the really big strides, he said. "I would say the industry underestimates how hard it is to improve the gas mileage," Kuttner said during the Plastics in Lightweight Vehicles conference. "As you get beyond 50 miles per gallon, it gets really hard. From 50 to 60 is hard. Sixty to 70 is much harder, and 70 to 80 is almost impossible." Kuttner joined Tata Technologies Ltd. designers Peter Davis and Raymond Peters, and Gregg Peterson from Lotus Engineering, to talk about super weight savings, during the conference, organized by Plastics News Nov. 6-7 in Livonia.