The thin metal grooves in escalator stairs might make the entire structure look extra dangerous, but they’re actually there for your safety.
As George R. Strakosch writes in The Vertical Transportation Handbook, the steps are cleated “so that people who ride with their toes against the riser will not have their soft shoe soles drawn between the steps as the steps straighten out.”
In other words, the grooves allow ascending steps to merge into a flat surface at the top of the escalator with minimal space between them. That way, the edge of a flip-flop or a runaway plastic bag won’t get sucked into the structure. According to Reader’s Digest, the (often yellow) strips of hardware with comb-like metal teeth that run along the top and bottom edges of escalators are there for the same reason. As the stairs disappear back into the depths of the escalator, these aptly named comb plates keep out anything that shouldn’t go with them.
Since escalator technology isn’t quite advanced enough to have comb plates toss that trash into the nearest garbage can, it’s still up to us to dispose of any litter a comb plate has pushed aside. But the most important part is that it’s been barred from entering the underbelly of the machine, where it could cause the escalator to break down.
The grooves also prevent liquids from pooling on the surface of the stairs, making escalators puddle-free—and possibly even safer than a regular set of stairs, at least on a rainy day.
[h/t Reader’s Digest]