As a result of the need to increase payload and flexibility of rigid haulers and ADT'S, as well as the requirement for spreading of loose material, the ETT bottom dumpers were developed. Used mostly in coal mines for both coal and coal discard, variations are also used in the salt mining industry, potash and soda ash mines. These robust off-road trailers increase the versatility of the haulers and allow greater payloads particularly in short haul applications.