Soon after the construction of the first narrow gauge lines, the problem arose that freight had to be reloaded at the transfer stations. A search was thus made for a better solution, and one of these solutions was to reload complete standard gauge cars on so-called roller carriers. A roller carrier is a small narrow gauge wheeled vehicle on which a wheelset of the standard gauge is loaded. Two roller carriers are thus required for a two-axle car. The roller carriers were in some cases equipped with the appropriate braking system of the narrow gauge line (compressed air, suction air, cable brakes), but there were also roller carriers without brakes. As a rule, only freight cars were loaded on roller carriers. It was not customary with passenger cars. Even today, roller carriers are still used to load freight cars – above all in Switzerland.