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In theory,e-commerce can be greener than a bunch of shoppers making personal trips in their own cars: Consolidating products and delivering them on one route to a bunch of homes requires fewer miles on the road. In a 2012 study, University of Washington professor Anne Goodchild found that grocery delivery can cut between 80% and 90% of carbon emissions, for example, compared to consumers going to pick up their items on their own. However, she says, that calculus changes significantly if items are coming from further away and have to be sent immediately, which creates fewer opportunities for lumping deliveries together.