The smaller carbon footprint, or wheel print, of automatic delivery robots can encourage consumers to use them when ordering food, according to a new study. The suitcase-sized, self-driving electric vehicles are much greener than many traditional food delivery methods because they have low, or even zero, carbon emissions. In this study, participants who had more environmental awareness and knowledge about carbon emissions were more likely to choose the robots as a delivery method. The green influence went away though when people perceived the robots as a high-risk choice — meaning they worried that their food would be late, cold or otherwise spoiled before it arrived.