Why Do Escalator Steps Have Teeth?

Escalator steps “have teeth” because modern escalators are engineered to keep riders safe at the exact moment steps transition from moving to stationary—and because the machinery must prevent objects (and people) from getting trapped at the comb plate and side gaps. The teeth-like grooves on step edges interlock with a comb plate at the top, lifting small items out of the way as the steps arrive. That design reduces jams and makes it safer for riders to step off forward, where a smooth, continuous surface would otherwise create dangerous snag points.

The deeper story behind escalator safety is that the Rome disaster on October 23, 2018—when a crowd surged onto a descending escalator at Rome’s Republica station—was not a failure of physics so much as a failure of safeguards and maintenance. Investigators reconstructed a chain reaction: the growing passenger load increased torque demands until the main motor reached its limit and the drum began to slip. Safety systems then activated in sequence—power cut via a safety relay, followed by a main brake meant to clamp the drum, and finally an auxiliary brake designed to bypass the motor and directly lock the drive shaft. Yet each layer underperformed.

Tests after the incident found the main brake’s stopping power was only about 37% of the manufacturer’s specification. When the auxiliary brake triggered, investigators discovered it had been partially disabled: plastic straps had been tied around one of the two brake wedges, preventing it from engaging. With that last mechanical backstop weakened by roughly half, the escalator continued accelerating until the steps plummeted, injuring 24 people.

Even more damning, the system’s error logs showed critical malfunctions had been turned off. Investigators concluded fault codes were disabled on purpose, meaning dangerous conditions could develop without leaving a trace for operators. Maintenance records were also incomplete, with evidence of major work that did not appear in official documentation. The technical findings pointed away from manufacturing defects and toward neglect and falsification.

Criminal investigation traced responsibility through contractor changes and uncovered coordination between Metro Roma and Rome’s transit authority ATAC. By September 2019, suspects were named and managers suspended. Prosecutors alleged safety devices were deliberately sabotaged to avoid shutdowns, with fraud and obstruction used to cover it up. A wiretap recording attributed to ATAC manager Renato Domico captured a callous framing of risk—treating potential failures as a numbers problem rather than a human one.

That human factor ties back to the engineering lesson: escalators are built with large safety margins and, when properly maintained, catastrophic failures are “vanishingly small.” Modern escalator design also includes features that improve efficiency and safety, such as regenerative braking on downward escalators using AC induction motors, which can generate electricity when resisting speed increases. But the Rome case shows that even robust engineering can be undermined when maintenance systems fail—especially when safeguards are disabled and records are falsified.

The transcript ultimately links the “teeth” at the step edge to a broader theme: escalators work because multiple layers—mechanical interlocks, comb plates, skirt brushes, handrail drive calibration, and braking logic—are designed to protect people during transitions. When those layers are respected and maintained, the system is remarkably reliable; when they’re tampered with, the consequences can be catastrophic.