In modern
graffiti terminology, a holy roller refers to a
railroad car designed to transport automobiles. These enormous "
auto-rack" cars are usually around 20 ft. tall and over 90 ft. long, and their flat sides make them perfect canvases for graffiti
pieces or
productions.
Most auto-racks have small holes punched through their sides for ventilation. For this reason, care must be taken that the car is empty when painting, so that the inevitable overspray does not damage its contents.