The simile “lay down / to sleep like a snow-covered road / winding through pines” refers to—

The simile “lay down / to sleep like a snow-covered road / winding through pines” refers to death. To be more exact, to death of the author's father. The message that author wanted to convey is to show how people can pass through their loss and to represent all the loneliness of death, comparing it to the loneliness of the winter road, empty and deserted. 

Dhope this /works