If you've ever tracked a package online and saw that it was "out for delivery" for what felt like forever, you already understand that the last mile problem is inefficiency. That's because the final leg of shipment typically involves multiple stops with low drop sizes.
In rural areas, delivery points along a particular route could be several miles apart, with only one or two packages getting dropped off at each one. In cities, the outlook isn't much better; what urban areas make up for in stop proximity is quickly negated by the near constant delays of traffic congestion.
The costs and inefficiencies of the last mile problem have only been further compounded by the continuous rise of e-commerce in US retail sales, which has dramatically increased the number of parcels delivered each day, as well as raised customer expectations to include not just fast, but also free, delivery.