 This pattern of fuel shifting explains why emission rates tend to be higher at night and lower during periods of peak demand in the morning and evening.In February 2014, the Automotive Science Group (ASG) published the result of a study conducted to assess the life-cycle of over 1,300 automobiles across nine categories sold in North America.The study found that among advanced automotive technologies, the Nissan Leaf holds the smallest life-cycle environmental footprint of any model year 2014 automobile available in the North American market with minimum four-person occupancy.