rollbock

thumb|right|Standard gauge goods wagon (freight car) on Rollbock, gauge

Rollbocks, sometimes called transporter trailers, are narrow gauge railway trucks or bogies that allow a standard gauge wagon to 'piggyback' on a narrow-gauge line. The Vevey system enables a coupled train of standard gauge wagons to be automatically loaded or rolled onto Rollbocks, so that the train can then continue through a change of gauge.