Apparatus (10) monitors a railroad crossing (X) for the presence of an object (H, V, A) in the crossing. The apparatus determines if an object is of sufficient size to damage to a train (1) approaching the crossing, and provides an alarm (Sa) to an approaching train so it can be timely halted. This prevents injury to people or other objects in the crossing, or to the train and its occupants. A camera (14) continuously views the crossing to obtain images of the crossing. An image processor (28) processes images, establishes the presence of objects in the crossing, and determines the size of the object. If appropriate, an alarm (26) is activated and an alarm signal is sent to the train through a relay (36) transmitter (44), and on board receiver (46). An audio alarm (48) on the train is sounded in response to receipt of the signal. The apparatus is unmanned and performs its monitoring function in a non-invasive manner by which its operation does not interfere with that of vehicles, pedestrians, or barriers (G) which may also be in place at the crossing.