If the employees in charge of any railroad engine or train fail to give the signals required by law on approaching a grade crossing of a public highway not protected with an automatically operating gate, operating wigwag signal or other operating electrical or operating automatic crossing protection device, the fact that a traveler on such highway failed to exercise due care in approaching such crossing shall not bar recovery for an injury to or death of such traveler, nor for an injury to or the destruction of property in his charge, where such injury, death, or destruction results from a collision on such crossing between such engine or train and such traveler or the property in his charge, respectively; but the failure of the traveler to exercise such care may be considered in mitigation of damages.