Abstract: A passenger carrying motor vehicle safety system for monitoring a space underneath the vehicle includes a photodetector assembly for generating a light beam and sensing interruptions in the light beam. A switch which is energized by the opening of the passenger door of the motor vehicle, activates the safety system. Holding contacts maintain the system in the activated state until the system is reset by the driver. A system reset switch, which is located within reach of the bus driver on the inside of the motor vehicle, is provided to reset the system so long as it has not been tripped. A trip reset switch, which is located on the outside of the motor vehicle, is provided to reset the system after it has been tripped.