1. Why Escalator Steps Stay Horizontal on the Slope
On the inclined section of an escalator, each step moves along with its top surface kept horizontal. At the entrance and exit, the horizontal steps line up at the height of the floor and head toward the comb. The arrangement of wheels and rails under the steps is involved in both of these states [2]. Below, we go through the step structure, the rails, the entrance and exit, the comb, and how the escalator came about.
2. How Four Wheels Under Each Step Let It Move Smoothly
The step (or tread) has two wheels (rollers) on the front side and two on the back side. Thanks to these wheels, the step can move smoothly [1]. An excerpt from a Ministry of Land, Infrastructure, Transport and Tourism document states that the wheels run on guide rails installed on the frame (truss) [3]. It is easier to imagine if you think of the step not floating in the air, but moving along on rails underneath. At the edge of the step, there are also protrusions (cleats) that mesh with the "comb" at the entrance and exit. We will deal with these in a later section.
3. How Two Rails Guide the Front and Back Wheels
There are two rails. One guides the front wheels, and the other guides the back wheels [2]. According to the English Wikipedia, on the straight inclined section, the gap between these two rails is at its widest. At this point, the back of the step is oriented at 90 degrees relative to the next step, lining up like a staircase [2]. The mechanical reason why a wide gap between the rails keeps the top of the step horizontal could not be confirmed from these sources alone. Manufacturers' technical reports would be the place to check.
4. How the Two Rails Come Together at the Entrance and Exit
According to the English Wikipedia, as the entrance and exit approach, the two rails come closer together, and the front and back wheels become almost in a straight line. The steps line up as a series of flat boards and can go around the curve [2]. On how many steps stay horizontal there, the Tokyo Metropolitan Government advisory council materials introduce a "3-step horizontal step," which increased the horizontal section from about 1.5 steps' length to 3 steps' length, as one of the safety measures [1]. That doubles the horizontal section. Not all models have 3 horizontal steps. Based on the wording explicitly stated in the materials, the aim of lengthening the horizontal section is a safety measure, while the effect of increasing the margin for boarding and alighting involves speculation.
5. How the Comb Plate Interlocks with the Grooves in the Steps
At the edge of the floor at the entrance and exit, there is a plate called a comb. It interlocks with the grooves on the top surface of the step [1]. Because the protrusions on the step and the protrusions on the edge of the comb interlock, the gap between the step and the comb becomes small [1] [2]. In the unlikely event that a foreign object gets caught and excessive force is applied, the comb is generally made of plastic, so that the tips of its teeth break rather than hold against the force [1].
6. The First Practical Escalator and the Origin of the Name
The first practical escalator is said to have been installed by Jesse Reno at Coney Island in New York in 1896. It was a belt-like device with a 25-degree incline and metal protrusions, which was a different shape from today's "flat steps" [2]. After that, Charles Seeberger advanced the design of flat steps and is said to have made the first commercial escalator with the Otis Company in 1899. The steps continued to move horizontally at the ends before disappearing under a triangular dividing plate [2]. This machine is said to have won a first prize at the 1900 Paris Exposition. The English Wikipedia states that the name "escalator" was created by Seeberger choosing scala (stairs) from a Latin dictionary as the root. It is not a combination of the word "elevator." All of this comes from the English Wikipedia, and other sources may tell it differently, so please treat these details as "said to be" rather than certain.
7. How to Investigate Escalator Steps Yourself at a Station
You can try counting how many horizontal steps continue at the entrance and exit at a station or commercial facility, from a spot where you do not get in the way. Compare different models: some may have 3 horizontal steps and some may not. The sources used here do not tell us how common the 3-step type is, so your own observation is the clue. Do not go near the edge of the steps or the comb, and watch from a spot that does not block the flow of people. To go deeper, look for manufacturers' technical reports and national or local government safety materials, and check the explanation of the gap between the two rails in primary sources. This article relies on an English-language explanation for that point.