By 2017, Lux Research predicts that more than 8 million cars in North America will be equipped with stop-start systems, a technology that has already gained popularity in Europe and Japan. Stop-start systems automatically shut off a vehicle’s engine when stopped in traffic, improving fuel economy by up to 12% and reducing exhaust emissions. AAA automotive experts believe that while stop-start systems can improve vehicle fuel efficiency, they also can affect HVAC performance. Also, the larger batteries required to run the systems are more expensive to replace. Hybrid cars and some premium-segment vehicles currently feature stop-start systems, but AAA predicts that the technology will soon see widespread applications as OEMs prepare to meet the 2016 U.S. Corporate Average Fuel Economy (CAFE) standards.