I have a book on diners (Classic American Diners), which starts with their history as lunch wagons...sort of a trailer setup. The first known one was in 1872 in Providence, RI. They started to be mass produced in 1887. When cities started scrapping old horse-drawn trolleys, they were sold cheaply for converting into lunch wagons. Most of these were shoddy establishments, and for a while, gave lunch wagons a bad name. Because later diners were modeled after RR diners, the name "diner" started being used in the early 1920s.