The Straight Road is the route that leaves the earth's curvature through sky and space to the ethereal land of Aman.
The Straight Road, so called because it follows the old path across Belegaer from before the Akallabêth when the Flat World was made Round, is only kept open to Elves, who are allowed to sail to it on their ships by a special grace of the Valar.
A ship departing on the Straight Road, when observed from the shore, would slowly become smaller to sight until it disappeared in a point, and not drop behind the horizon[source?].
Like Tuor and Amandil attempted to reach Aman, also some mortals traveled the Straight Road. Bilbo Baggins and Frodo Baggins sailed into the West on the White Ship, and followed by Samwise Gamgee who sailed alone, but presumably found his way.
In most recent history there has been an Ælfwine.