It connects the San Juan neighborhood of Río Piedras to downtown Salinas indirectly around the eastern coast of the island.

While other roads connect San Juan, it runs the coastline of Puerto Rico east of San Juan, beginning in Río Piedras near Santurce (where it is known as the Avenida 65 de Infantería) and goes to Fajardo where it goes south paralleling the coastline to Humacao and Maunabo.

[4][5] PR-3 begins at an intersection with PR-1 in San Juan as the three lane 65th Infantry Regiment Avenue.

Heading east through San Juan, Highway 3 functions as an urban boulevard with both at-grade and grade-separated intersections becoming decidedly suburban in character past the PR-26/66 overpass near downtown Carolina.

In Maunabo and south Yabucoa, PR-3 is not the main "at-grade" artery since it goes up in the mountains.