An escalator drive assembly (30) includes a sensor that facilitates detecting when the normal drive assembly operation is interrupted, such that a brake should be activated. In one example, a sensor member (40) in the form of a flange (42) is associated with a drive pulley (34) and normally rotates in unison with the drive pulley. When there is a failure in the normal operation of the drive mechanism, however, there is a resulting relative movement between the sensor member (40) and the drive pulley (34). Such relative motion preferably activates a switch (80) that provides a signal that indicates a failure of the normal operation of the drive mechanism (30). Another example sensor includes a sensor member (202, 212) that engages a drive belt (35). If the belt (35) breaks, the sensor member (202, 212) moves to provide an indication of the broken belt condition. Various braking application modes are possible using the invention.