What is the purpose of the brushes at the side of an escalator?

No, they are not there to clean your shoes but instead, they are there for a safety reason. This long continuous brush called "Deflector brush" or "Skirt Brush" is made of stiff bristles that runs up the sides of the escalator just above the step level. It is designed to deflect objects like garments, shoes and other things away from the gap between the steps and the side wall. They also work as an indicator to tell passengers that they are close to the step's edge.