In its simplest form a zip-line consists of a pulley that rides upon a suspended cable. The cable is generally stretched between a pair of vertical mounts serving as cable supports. Preferred supports include large trees, which may be selected from those growing on a slope, and towers, which may be erected upon a hillside or in a field. Generally one mounting point will be selected to be higher than the other by a suitable differential of elevation. Since the cable determines the trajectory of the pulley, it may be referred to as a guide cable.
For most applications the simple pulley is replaced by a trolley that rests upon the cable and is fitted to carry a payload as it moves freely along the length of the guide cable. When adapted for amusement purposes, a simple zip-line enables a user propelled by gravity to traverse from one end of the guide cable to the other, generally from the upper end to the lower end along an incline, by holding on or attaching to the freely moving trolley. The cable is usually made of high tensile steel, as would be used for a tram, with the cable thickness being sized according to the length of the run and size of the load. While some zip-lines are used in the logging industry, there is a growing interest in zip-lines for amusement or entertainment purposes, especially as a means to access unusual areas, such as a rainforest canopy, or in outdoor adventure camps.
In its extended form the presently described system relates to overhead trolleys, especially zip-lines and other cable-supported tram-like systems. A typical recreational setting, such as a park, will often use multiple cables to carry passengers down, or up, a slope with each cable being generally straight, having no mid-line turns. When the direction of a zip-line within a course is to be altered, the riders must disembark at the end of one cable segment and re-embark at the start of another, with alternate transportation, such as foot traffic or motorized cart between those two endpoints. Such discrete segmented operation is required by conventional cable systems because of the problems associated with guide cable supports or terminations interfering with the unobstructed movement of a trolley as it passes from one segment to the next.