Low gasoline prices and continuing performance issues have slowed the growth of electric car sales. But that has not stymied progress in electrifying larger vehicles, including garbage trucks, city buses, and medium-sized trucks used by freight giants like FedEx.The clang of garbage cans will still probably wake people way too early in the morning. But in Santa Rosa, California, at least, the roaring diesel engine will be quiet, replaced by a silent, electric motor.