The National Highway System of Puerto Rico (not to be confused with the
National Highway System of the United States) consists of of highway and roadways of four types: primary, urban primary, secondary, and tertiary. All Puerto Rico expressways are signed either primary or urban primary. Puerto Rico's
controlled-access highway may be an
expressway, an arterial highway with full or partial control of access. Expressways with full control of access are called
freeways. If the freeway charges a toll for its use, it is called an . In 2009, primary routes were about 14% of the total Puerto Rico Highway system mileage, secondary were about 30%, and tertiary about 56%. As a road or highway goes from being part of one network to another, it maintains its same number but is then marked with its new network shield type. An example of this is when
PR-1, connecting
Ponce and
San Juan, is signed as urban primary inside the Ponce city limits, then is signed as secondary in Ponce's rural barrio
Capitanejo, and then is signed as an urban primary road, on its entry into the town of
Santa Isabel. This means that regardless of the amount of digits a road number may have, any road could be signed as primary network, urban primary network, secondary network or tertiary network all dependent on the area it goes through.
Primary network highways Primary roads are numbered in the 1 to 99 range and are distributed randomly throughout the island. The primary highway marker has a white background and a blue shield with white lettering. A primary road's purpose is to facilitate movement of passengers and freight between major regions of the island. PR primary 1.svg|Highway shield for primary section of PR-1 PR-54 West and East junction with PR-744.jpg|
PR-54 West and East junction with
PR-744 in
Guayama Urban primary network highways The purpose of urban primary highways are to complement the primary network inside the
eight metro areas: San Juan, Ponce, Mayagüez, Arecibo, Aguadilla, Humacao, Caguas and Guayama. Some highways may be designated as R for
Ramal, branch in Spanish, such as
PR-2 which has several R designations along its length usually as a branch or loop that goes through the center of a town while the highway continues around and on to the next municipality. This is due to the fact that the original PR-2 went through every town center but these sections were bypassed and designated R to alleviate congestion. The urban primary marker has black lettering on a white shield over a black background. Secondary roads are numbered in the 100 to 299 range and generally follow a grid pattern. They begin from the southwest portion of the island with
PR-100 and increase in number in northeasterly fashion. PR-100 is located in the southwestern town of Cabo Rojo, while
PR-198 is in
Juncos, Las Piedras and Humacao in the eastern part of Puerto Rico. As of February 2014, the highest secondary highway number assigned was 252 (
PR-252), located in the northeastern municipality-island of
Culebra.
PR-199 lies in Guaynabo and San Juan, not adhering to the pattern. PR secondary 1.svg|Highway shield for secondary section of PR-1 For your safety, driving in Puerto Rico sign.jpg|"For your safety" tips for driving in Puerto Rico sign Puerto Rico Highway 145 in Torrecillas, Morovis, Puerto Rico.jpg|
PR-145 in Torrecillas, Morovis
Tertiary network highways Tertiary highways or roads provide access to a municipality's main urban area from peripheral communities. The tertiary highway marker has a white circle (white black lettering) on a black background. Roadways that have both their terminus within the same municipality are called tertiary roads and are, by convention, numbered PR-300 through PR-9999. The road marker in the shape of the island of Puerto Rico can also still be seen on some roadways.
Three-digit tertiary roads Tertiary highways also known as local highways, follow a general numbering pattern. The northern area in the region west of
San Juan contains even-numbered roads, while the southern area contains odd-numbered ones. This changes in the region to the east of San Juan as both northern and southern areas are covered by roads of the 900-999 grid. The diagram illustrates the organization of these roads and may help better understand the distribution. Some roads may start or end among differently numbered areas like in
Ciales, a mountainous municipality, it has highways in both the 600-699 grid and the 500-599 grid. Another example is in the southeastern municipality of
Maunabo where the 700-799 grid overlaps the 900-999 grid.
Vieques, an offshore island-municipality, has some highways in the 900-999 grid but also has roads in the 200-299 category that is shared with
Culebra, another offshore island-municipality which has
PR-250 and
PR-251 as its main routes. Ellipse sign 1.svg|Highway shield for tertiary section of PR-1 PR-438 Cuesta de Magos seen from Calabazas, San Sebastián, Puerto Rico.jpg|
PR-438, a steep roadway, seen from
Calabazas barrio,
San Sebastián Barrio Espino, Lares, Puerto Rico, PR-435 junction with PR-124.jpg|PR-435 and
PR-124 highway junction in
Espino, Lares
Four-digit tertiary roads Some roads are numbered with four digits, for example,
PR-5506. These are branches, or
spurs, of tertiary roads by the same last three digit number. Thus, PR-5506 is a branch of
PR-506. They are often
dead end branches, and are common in the mountain regions of the main island. Sometimes they are
loops branching off the main road, eventually connecting back to the same main tertiary road. The “fourth” digit is generally a repeat of the first digit of the main tertiary road in question. Thus, a branch of
PR-301 would be signed
PR-3301, with the added
3 prefixing the number of the main tertiary road associated with the spur, 301, because
3 is the first digit of the main road. When the road has more than one distinct spur, an additional unrelated digit is used (example, PR-4301). PR-6622 and PR-617 signs in Morovis, Puerto Rico.jpg|PR-6622 and PR-617 signs in Morovis Puerto Rico highway 6685 in Manatí, Puerto Rico.jpg|
Puerto Rico Highway 6685 in
Manatí PR-9974 in Mariana, Naguabo, Puerto Rico.jpg|Kilometer 1.0 on a road in Naguabo ==Interstate Highway System==