Side opening elevator doors (also called single-panel or SO doors) are automatic sliding doors where one or more door panels slide to one side to open. Single-panel side opening (1SO) is common for small cabins and low-traffic applications; two-panel side opening (2SO) provides a wider opening. Compared to center-opening doors, side-opening doors require less clear overhead space for the door operator and are often preferred for smaller cabin widths, retrofit installations, and service or freight elevators.