Puerto Rican addresses can be a little confusing, with several systems employed using a combination of English and Spanish. All roads have a number: you’ll often see these prefixed by “Carr” or Carretera (meaning “highway” or “route”) when written down, though you rarely see this on actual road signs, where just the number or the “PR” prefix is more common. Note that a sign reading “INT 3” means that an intersection with PR-3 is coming up, not that you are currently driving on PR-3.
In many places street numbers are not used, and locations are either described (esquina means “corner”) or given a kilometre reference. A location at PR-3 km 2.1 would be 2.1km from the beginning of PR-3, though in practice it’s hard to know where this is or even which end of the road is considered the beginning. In some places useful markers on the roadside show the distance every tenth of a kilometre, but these are becoming rarer. It’s always faster to call your destination for directions.