Traditionally, start-stop technology is common on hybrid vehicles. This technology allows the car to turn the engine off when it stopped at a red light or in traffic in and start backup automatically. It sounds good in theory, but in practice, some of the hybrids I've driven have quite a lag between the engine turning off the engine coming back on.
Ford has announced that it will make start-stop optional with a price of only $295 on the 2013 Fusion. The option will only be available on 1.6-liter EcoBoost equipped Fusion and promised to save as much as 10% on fuel economy for some drivers with 3.5% average.