jump truck
n.— «The workday for a Chicago area Good Humor man back in 1969 began at one central location with 175 men, each dressed in white, climbing into 175 identical white trucks, and going out on their routes. The open air trucks were often called “jump trucks,” because the men would have to jump out to serve customers.» —“Bells that kept us in Good Humor” by Chris Stach Landmark (Oak Park, Illinois) Aug. 7, 2007. (source: Double-Tongued Dictionary)