The grooves in escalator stairs serve a few key purposes, the primary one being safety.
You might be a little freaked out over escalator stairs just because they have metal grooves in the steps. Although it may look strange, they are actually there to keep you safe.
The author of The Vertical Transportation Handbook, George R Strakosch says that the cleated steps are there “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 layman’s terms, when the steps merge into a flat surface, the grooves prevent too much of a gap that would lead to danger. If you happen to have a bag or the edge of your flip-flop near the edge, they will be safe. Readers Digest reports that the strips of hardware with metal teeth that run at the top and bottom of escalators serve the same purpose. The stairs are constantly moving back into the escalator and the ‘comb plates’ ensure that nothing else goes back that shouldn’t.
If there is any litter that happens to get pushed aside by the comb plate, it is going to remain there until somebody is kind enough to pick it up and throw it in the trash. The fact that it is there lets you know that it did not make it into the workings of the machine, resulting in a breakdown of the escalator.
One other feature of the grooves is to keep liquid from pooling on the stairs. That is really a benefit to limit slip and fall accidents or to keep your feet dry on a rainy day.