An allusion is a literary device in which one work refers to another work. Here are a few examples of allusions some might perceive in "The Road Not Taken."
The notion of representing life as progress down a road is common in literature. Many classic works such as Bunyan's Pilgrim's Progress and Browning's "Childe Roland to the Dark Tower Came” involve people walking along roads and making decisions about their routes which have significant consequences for their future lives.
The most obvious parallel, though, is Prodicus' "Choice of Hercules," a display oration by the distinguished fifth century Greek sophist Prodicus of Ceos reported in Plato's Protagoras. In this story, Hercules must make a choice between Vice, who offers him a short, easy, well-paved road sloping downwards, and Virtue, who offers him a steep, harsh road sloping upwards. A later work by Lucian, a second century sophist, "Rhetorum praeceptor" ("The Teacher of Rhetoric") offers a similar choice, with more detailed physical descriptions of the two roads.