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a motorless wheeled vehicle towed by an automobile or tractor truck.
A trailer usually has a closed body or a platform with sideboards. Special-purpose trailers have a body designed for specific freight. “Broken-up” trailers are used in hauling long loads; they are connected to the prime mover by the load itself. Trailers are also used as mobile installation bases for various equipment, such as compressor stations. The load-carrying capacity of single-axle trailers usually is no more than 2 tons. Two-axle trailers can carry 8 tons, and multiaxle trailers with large loads that cannot be broken up can manage 20–50 tons or more. Trailers are connected to the tractor by a draft bar. To lower the height of the load and to improve stability, trailers are sometimes built with a low frame. Trailers are equipped with outlining lights.