@ Phil 11:04 Feb 22
In today's standard rail vehicles for passenger transport, there is often a contact strip that initiates a backward movement when closing if there is a person or an object in between. This is independent of whether the door is a sliding door or a folding door. In addition, the closing time and the travelled path can be monitored. The door then attempts to close again. If this fails, the train conductor asks the passengers to release the door or to stop boarding. As a former railwayman, I was often able to observe this.
Whether you record the time as a function of the path or the path as a function of the time is irrelevant. It is only a coordinate transposition (s = f(t) to t = f(s). | 
peer agreement (net): +2