Transporter wagons

A transporter wagon, in railway terminology, is a wagon (UIC) or railroad car (US) designed to carry other railway equipment. Normally, it is used to transport equipment of a different rail gauge. In most cases, a transporter wagon is a narrower gauge wagon for transporting a wider gauge equipment, allowing freight in a wider gauge wagons to reach destinations on the narrower gauge network without the expense and time of transshipment into a narrower gauge wagons.

This is an attempt to overcome one of the primary problems with differing gauge systems—gauge incompatibility. However, it means that the narrower gauge network must be built to a structure gauge large enough to accommodate the loading gauge of the wider gauge equipment, negating one of the cost advantages of a narrower gauge construction. Additionally, a large wider gauge wagon balanced on a narrower gauge transporter wagon is not very stable, and is generally restricted to low speeds of 15 mph (24.1 km/h) or so.

Transporter wagons have seen varying popularity. They were quite common in Germany (where they are called Rollwagen), Austria, Switzerland (here called Rollschemel in German and trucs transporteurs in French) and Sweden.

Transporter wagons were uncommon in North America, where the practice of exchanging trucks was more common, as was at one time the case on CN's Newfoundland Railway at Port aux Basques. They were used on the Paw Paw Railroad of Paw Paw, Michigan for a short time, and on a short stretch of track of the defunct Bradford, Bordell and Kinzua Railroad by lumberman Elisha Kent Kane. They were used in the United Kingdom on the Leek and Manifold Valley Light Railway.

...
Wikipedia