Manila's rapid urbanization. The metropolis is resolving this problem through the completion of missing road links or through the construction of connector roads. The radial and circumferential road system are being supplanted by a new numbered highway system implemented by the Department of Public Works and Highways, and new signage are being placed with its implementation. Expressways are being assigned numbers with the E prefix. National roads are assigned 1 to 3 digit numbers, except for those classified as tertiary national roads. An important circumferential road is the Circumferential Road 4, with the Epifanio de los Santos Avenue as its major component. It traverses the cities of Pasay, Makati, Mandaluyong, Quezon City and Caloocan. Line 3 follows the alignment of EDSA, from Taft Avenue in Pasay up to TriNoma, terminating before it reaches Caloocan. Circumferential Road 5 serves the people near the regional limits of Metro Manila and also serves as an alternate route for Circumferential Road 4. Prominent radial roads include the Radial Road 1, composed of Roxas Boulevard and the Manila–Cavite Expressway (Coastal Road) that connects Metro Manila to Cavite, Radial Road 3 or the South Luzon Expressway that connects Metro Manila to Laguna, Radial Road 6, composed of Aurora Boulevard and Marcos Highway that runs up to Rizal and Radial Road 8 or the North Luzon Expressway that serves as the gateway to the north. The Skyway serves as the region's main expressway, directly connecting the North Luzon Expressway and the South Luzon Expressway. It also enables access to Ninoy Aquino International Airport via the NAIA Expressway (NAIAX). The Skyway is the first fully grade-separated highway in the Philippines and one of the longest elevated highways in the world with a total length of approximately . Other expressways such as the Manila–Cavite Expressway and Muntinlupa–Cavite Expressway also connect Metro Manila to its surrounding areas. The development of roads, highways and expressways are based on the Metro Manila Dream Plan. Ongoing projects in the dream plan include the rehabilitation of EDSA, Skyway Stage 3 and the construction of the missing road links for the circumferential roads (e.g. Taft Avenue Flyover, Metro Manila Interchange Project Phase IV). Railway systems Rail transportation in the Greater Manila Area is a major part of the transportation system in Metro Manila and its surrounding areas. It consists of the Manila Light Rail Transit System, Manila Metro Rail Transit System, and the PNR Metro