Rollbocks, sometimes called transporter trailers, are pre-coupled narrow gauge transporter trucks or bogies that allow a coupled train of standard gauge wagons to be automatically loaded or rolled onto so that the train can then continue through a change of gauge.
The system uses a narrow gauge rail running in a pit that is built in the middle of a standard gauge track. It allows the Rollbock bogies to 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 (Rollwagen) designed to keep costs down by avoiding the need for a complete wagon.
The original invention goes back to the Rollwagen of the Schweizer Maschinenfabrik Winterthur (Swiss Locomotive and Machine Works, Winterthur) or SLM patented in 1880. It is a simple system for light loads that found applications even when the superior Langbein system was invented in 1881 by the Maschinenfabrik Esslingen (Esslingen Engineering Works) named after Paul Langbein being the director of the facilities in Saronno, Italy.
The Langbein System uses claw pairs to form a yoke around the axles of the standard gauge bogies. With the bogies pulled out of the pit the standard gauge wheels can sink to the Rollbock to find support. This method enables the Rollbock wagons to traverse curves as sharp as 15 m (49.2 ft) radius and, when fully loaded, they could be moved over narrow gauge tracks at a safe speed of 13 mph or 21 km/h.
In 1974 a renovation of the concept was developed for Yverdon–Ste-Croix railway in Switzerland. Unlike the Langbein System the Vevey System requires no manual intervention to fixate the standard gauge axles over the narrow gauge bogies. Many modern Rollbock applications have since converted to the Vevey System. The Vevey Technologies company was bought by Bombardier in 1998.
They are used extensively in Switzerland and in Spain, in the latter country to transport standard gauge vehicles on broad gauge lines (although the difference is small enough to allow variable gauge axles in some applications).
Until the 1990s the Rollbock sidings at Wernigerode 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 to transport china clay to Meissen.
However, it means that the narrower gauge network must be built to a structure gauge large enough to accommodate the loading gauge of standard gauge wagons, negating one of the cost advantages of a narrower gauge construction. The system was tested for the narrow gauge railways in Saxony around 1900 but it found only rare application - tracks requiring higher transport capacity were rebuilt to standard gauge instead. However it is also possible to use the wagons of the narrow gauge loading gauge type built with standard gauge axles which allows them to run at full speed on standard gauge tracks piggybacking them on the short section in the mountains by Rollbock bogies. This application requires the receiver of the freight to be able to unload those wagons so they have found only limited use either.
- Jackson (2006), p. 290 - albeit Jackson uses the German plural here: Rollböcke.
- Jackson (2006), ibid.
- "Bombardier Transportation in der Schweiz - Geschichte" (in German). Retrieved 2012-12-16.
- Jackson, Alan A. (2006). The Railway Dictionary, 4th ed., Sutton Publishing, Stroud. ISBN 0-7509-4218-5.
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