A switchman lived in a small shack on one side of the river where he operated the controls to turn the bridge and lock it into place as the train crossed.  One evening as the switchman was waiting for the last train to cross, he looked off into the distance through the dimming twilight and caught sight of the train's light.  He stepped to the controls and waited until the train was in the prescribed distance before he was to turn the bridge. He started to turn the bridge into position, but to his horror, the locking device failed to operate.  He knew that if the bridge was not locked securely into position it would wobble back and forth at the ends when the train rode onto it, thus causing the train to jump the track and go crashing into the river. This happened to be a passenger train full of people. 

The switchman sped to the other side of the bridge where there was a lever which he would use to operate the lock manually.  He could hear the rumble of the train approaching.  Taking hold of the lever, he leaned backwards, applying all his weight to it, thus locking the bridge.  Many lives depended upon his strength. 

Then coming across the bridge from the direction of his control shack, came a sound that made his blood run cold! "Daddy, where are you?" His four year old son was crossing the bridge to look for him!   His first impulse was to cry out to the child "RUN!  RUN!" but the train was too close, the tiny legs would never make it across the bridge in time.  The switchman was about to let go of the lever and run to his son's aid, but suddenly realized that he would never get back to the lever in time.  Either the people on the train or his little son must die.