A pipeline roller coaster is a type of roller coaster where the trains ride between the tracks as opposed to a traditional roller coaster where they ride above them. The concept was first developed by Japanese ride company TOGO as the Ultratwister model. They built six installations of the design, four of which are still in existence. Arrow Dynamics created an alternate version of the concept, but it never made it past the prototype stage in development. Intamin developed a version known as the Spiral Coaster model, building only one installation, which is no longer in operation.