Puerto Rico Highway 15

Puerto Rico Highway 15 (PR-15), formerly Road No. 4 (Carretera #4), is a main highway connecting the municipalities of Guayama and Cayey in Puerto Rico. With a length of 25.80 km, it extends from PR-3 in downtown Guayama to PR-14 in downtown Cayey.

Route description
This highway consists of one lane in each direction for most of its length due to its rural characteristics. In Guayama, PR-15 begins at PR-3 junction in the city center. Then, it leaves the urban area and heads to the north, where meets with PR-179 and crosses the Río Guamaní though the Cayey Bridge before climbing the Sierra de Cayey mountains. In this municipality, PR-15 makes its way though Caimital, Palmas and Guamaní barrios before entering Cayey.

In Cayey, PR-15 makes its way though Jájome Alto barrio after crossing the Guayama municipal limit in the Sierra de Cayey. From this point, the highway continues to the north towards the urban area. Between Jájome Alto and Culebras Bajo barrios, PR-15 meets with the Ruta Panorámica, of which is part from PR-741 intersection to PR-7737 junction. After that, the road goes down the mountains through Quebrada Arriba and Monte Llano barrios until its junction with PR-1, where PR-15 enters the city center for make its final length until PR-14 intersection.

History
Originally, PR-15 was identified as Road No. 4, a spur route of the Carretera Central from Cayey to Guayama. As Road No. 4, Puerto Rico Highway 15 was built between 1886 and 1897, and changed its number to the current designation after the 1953 Puerto Rico highway renumbering, a process implemented by the Puerto Rico Department of Transportation and Public Works (Departamento de Transportación y Obras Públicas) that increased the insular highway network to connect existing routes with different locations around Puerto Rico. The entire length of PR-15 was listed on the National Register of Historic Places in 2020.