A system comprising: a conveyer , a sensor operationally directed to engage the conveyer , a controller for controlling the conveyer and the sensor , wherein the controller is configured to render a plurality of determinations including: a first determination that the conveyer is in an operational state, a second determination that first sensed data dynamically obtained from the sensor is indicative of a first passenger on the conveyer , a third determination to model shape of the first passenger , while the first passenger is on the conveyer , with a first nodal model , a fourth determination to track displacement differentials for the first nodal model , a fifth determination to identify from the differentials an occurrence of an alert condition with the first passenger , at an occurrence of an alert condition, a sixth determination to stop the conveyer , and the controller is configured to transmit first instructions to the conveyer to effect the sixth determination; charactized in that said first nodal model consists of nodes representing the first passenger and in that the controller is configured to determine an alert condition exists when: one or more horizontal displacement differentials and/or one or more respective horizontal differential rates are below a second threshold; and/or one or more total displacement differentials and/or one or more respective total differential rates are below a third threshold. a conveyer , a sensor operationally directed to engage the conveyer , a controller for controlling the conveyer and the sensor , wherein the controller is configured to render a plurality of determinations including: a first determination that the conveyer is in an operational state, a second determination that first sensed data dynamically obtained from the sensor is indicative of a first passenger on the conveyer , a third determination to model shape of the first passenger , while the first passenger is on the conveyer , with a first nodal model , a fourth determination to track displacement differentials for the first nodal model , a fifth determination to identify from the differentials an occurrence of an alert condition with the first passenger , at an occurrence of an alert condition, a sixth determination to stop the conveyer , and the controller is configured to transmit first instructions to the conveyer to effect the sixth determination; a first determination that the conveyer is in an operational state, a second determination that first sensed data dynamically obtained from the sensor is indicative of a first passenger on the conveyer , a third determination to model shape of the first passenger , while the first passenger is on the conveyer , with a first nodal model , a fourth determination to track displacement differentials for the first nodal model , a fifth determination to identify from the differentials an occurrence of an alert condition with the first passenger , at an occurrence of an alert condition, a sixth determination to stop the conveyer , and the controller is configured to transmit first instructions to the conveyer to effect the sixth determination; charactized in that said first nodal model consists of nodes representing the first passenger and in that the controller is configured to determine an alert condition exists when: one or more horizontal displacement differentials and/or one or more respective horizontal differential rates are below a second threshold; and/or one or more total displacement differentials and/or one or more respective total differential rates are below a third threshold. one or more horizontal displacement differentials and/or one or more respective horizontal differential rates are below a second threshold; and/or one or more total displacement differentials and/or one or more respective total differential rates are below a third threshold. <EOS>