Abstract: An escalator is formed of a plurality of steps traveling in a continuous conveyor between a pair of spaced apart skirt plates. Each step has lateral safety boundaries attached to the side edges thereof. Spring inserts are positioned between the outermost ribs of the tread plate and the riser of the step to maintain the safety boundaries in contact at all times with the skirt plates. Thus, differences in the distance between the skirt plates and deviations of the travel path of the steps are equalized and the air gaps between the skirt plates and the side edges of the steps are closed at all times. The material from which the safety boundaries are made is selected to provide the lowest possible friction losses and to prevent scraping noises during operation. However, the safety boundaries will wear down before the skirt plates and worn out safety boundaries can be replaced without having to dismantle the corresponding step from the step conveyor.