What should be the minimum depth of a tread on a moving stairway?

The minimum depth of a tread on a moving stairway is essential for safety and usability. A depth of 15 3/4 inches allows for comfortable foot placement and ensures that users can step onto and off the escalator without the risk of tripping. This dimension accommodates a diverse range of foot sizes and helps to provide stability while in motion. The depth ensures that the steps are neither too shallow, which could lead to instability, nor excessively deep, which may unnecessarily complicate foot movement.

Standards and safety regulations set by organizations such as the American National Standards Institute (ANSI) inform these dimensions, reflecting an understanding of human factors in design. Having a standard tread depth enhances user confidence and safety on moving stairways, making this dimension critical in construction and maintenance. Other options do not align with the established guidelines for tread depth, which is why they are not applicable in this context.