highest secondary highway number assigned so far (February 2014) is 252 (PR-252), located in the northeastern municipality-island of Culebra. A few roads “violate” this grid order; for example, PR-199 lies in Guaynabo and San Juan. Tertiary highways Tertiary highways also follow a general grid. Towns which do not border the Atlantic Ocean or the Caribbean Sea, especially in the mountainous area, may overlap this grid, for example Ciales may have both highways in the 600-699 grid and the 500-599 grid, depending where they begin further north or further south. Generally along the areas where the highways are, the lower the number, the more south it is. Culebra is the only town in Puerto Rico that does not fall in any of the regions, for only PR-250 and PR-251 are the main routes. The entire immediate metropolitan area of San Juan with the exception of Caguas falls in the 800 region, while the entire east coast (north and south) east of San Juan, Caguas and Patillas fall in the 900 region. This is because the eastern portion of Puerto Rico has a southeastern coast which goes to the west from Humacao, which roughly defines where the Vieques Passage and the Caribbean Sea meet along the coast. Yabucoa is in the exact south-southeast area and lies in the 900 region, while Maunabo overlaps the 700's and 900's regions. Vieques, an offshore island-municipality, has some highways in the 900 order. Some roads are numbered using 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 and 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). Interstates There are no Interstate-signed highways in Puerto Rico, but there are roadways that have received up to 90% of their funding from the