Importance of The railway bridge

This is the bridge the train went off of during a midnight crossing, killing all the passengers except two railway employees who were on the open back of the caboose. When Ruth and Lucille see Sylvie walking across the bridge, looking down at the water, they begin to realize how seriously disturbed she is and they fear that she will take her own life as their mother did. At the very end of the book, Ruth leaves Fingerbone late at night by following Sylvie across the bridge above the terrifying depths of lake.