The Rollbock system allows a coupled train of standard gauge wagons to be automatically loaded or rolled onto pre-coupled narrow gauge transporter trucks or bogies so that the train can then continue through a change of gauge. The Rollbock bogies go underneath the standard gauge tracks and as the Rollbock train is pulled out of the Rollbock siding each bogie picks up one axle of a standard gauge wagon as it rises out of the Rollbock pit. Thus two Rollböcke are needed for a twin-axle wagon. They were a development of the transporter wagon

Transporter wagon

A transporter wagon, in railway terminology, is a wagon or railroad car designed to carry other railway equipment. Normally, it is used to transport equipment of a different rail gauge...

 (Rollwagen) designed to keep costs down by avoiding the need for a complete wagon.

Also known as the Langbein system, this method enables the Rollbock wagons to traverse curves as sharp as 15 m radius and, when fully loaded, they could be moved over narrow gauge tracks at a safe speed of 13 mph/21 km/h.

They are used extensively in Switzerland

Switzerland

Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

 and in Spain

Spain

Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

, in the latter country to transport standard gauge

Standard gauge

The standard gauge is a widely-used track gauge . Approximately 60% of the world's existing railway lines are built to this gauge...

 vehicles on broad gauge

Broad gauge

Broad-gauge railways use a track gauge greater than the standard gauge of .- List :For list see: List of broad gauges, by gauge and country- History :...

 lines.

They are also still in use at Nordhausen

Nordhausen

Nordhausen is a town at the southern edge of the Harz Mountains, in the state of Thuringia, Germany. It is the capital of the district of Nordhausen...

 on the Harz Narrow Gauge Railways to transport limestone wagons from the narrow gauge to the DB system.

Until the 1990s the Rollbock sidings at Wernigerode

Wernigerode

Wernigerode is a town in the district of Harz, Saxony-Anhalt, Germany. Until 2007, it was the capital of the district of Wernigerode. Its population was 35,500 in 1999....

 were used every day to transport goods to and from the various metallurgical factories attached to the Harz Narrow Gauge Railways in the
immediate area. Similarly it was used extensively on the Saxon narrow gauge system west of Dresden

Dresden

Dresden is the capital city of the Free State of Saxony in Germany. It is situated in a valley on the River Elbe, near the Czech border. The Dresden conurbation is part of the Saxon Triangle metropolitan area....

 to transport china clay to Meissen

Meissen

Meissen is a town of approximately 30,000 about northwest of Dresden on both banks of the Elbe river in the Free State of Saxony, in eastern Germany. Meissen is the home of Meissen porcelain, the Albrechtsburg castle, the Gothic Meissen Cathedral and the Meissen Frauenkirche...

.

However, it means that the narrower gauge network must be built to a structure gauge

Structure gauge

The structure gauge, also called the minimum clearance outline, is the minimum height and width of tunnels and bridges as well as the minimum height and width of the doors that allow a rail siding access into a warehouse...

 large enough to accommodate the loading gauge

Loading gauge

A loading gauge defines the maximum height and width for railway vehicles and their loads to ensure safe passage through bridges, tunnels and other structures...

of standard gauge wagons, negating one of the cost advantages of a narrower gauge construction. One could of course use standard gauge wagons especially built to a smaller than normal loading gauge.