The smaller carbon footprint, or wheel print, of automatic delivery robots can encourage consumers to use them when ordering food, according to a Washington State University 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.

The findings, reported in the International Journal of Hospitality Management, indicate a way to promote the use of delivery robots.

"Much of the marketing focus has been on the functionality and the convenience of these automatic delivery robots, which is really important, but it would enhance these efforts to promote their green aspects as well," said lead author Jennifer Han, a doctoral student in WSU's Carson College of Business.

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