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.

With railways, a break of gauge occurs where a line of one track gauge meets a line of a different gauge. Trains and rolling stock generally cannot run through without some form of conversion between gauges, leading to passengers having to change trains and freight requiring transloading or transshipping; this can add delays, costs, and inconvenience to travel on such a route.