The Smithsonian has this really great article on the history of the postal truck and the criteria it uses for the purchase of new ones.
“The Long Life Vehicle, or LLV, marked a major change in how postal officials approached buying vehicles. Until the 1980s, when new vehicles were needed, officials combed through existing models for the best fit. This often resulted in vehicles that met some, but never all, of the demands of moving mail.
Finally officials decided to try something different. They created a set of criteria for the perfect letter carrier vehicle and challenged commercial vehicle industries to create a vehicle to order.”
Read the rest of the article on the Smithsonian Website…