MRT Line 3 (Metro Manila)

The Metro Rail Transit Line 3, also known as the MRT Line 3, MRT-3 or Metrostar Express, is a light rapid transit system line of Metro Manila, Philippines. Originally referred to as the Blue Line, MRT Line 3 was reclassified to be the Yellow Line in 2012. The line runs in an orbital north to south route following the alignment of Epifanio de los Santos Avenue (EDSA). Although it has some characteristics of light rail, such as the type of a tram-like rolling stock used, it is more akin to a rapid transit system owing to its total grade separation and high passenger throughput.

Envisioned in the 1970s and 1980s as part of various feasibility studies, the thirteen-station, 16.9-kilometer (10.5 mi) line was the second rapid transit line to be built in Metro Manila when it started full operations in 2000 under a 25-year concession agreement between its private owners and the Philippine government's Department of Transportation (DOTr).

The line is owned by the Metro Rail Transit Corporation (MRTC), a private company operating in partnership with the DOTr under a Build-Lease-Transfer agreement. Serving close to 550,000 passengers on a daily basis when MRTC's maintenance provider, Sumitomo Corporation of Japan, was handling the maintenance of the system, the line is the busiest among Metro Manila's three rapid transit lines, built with essential standards such as barrier-free access and the use of contact-less card tickets to better facilitate passenger access. Total ridership significantly exceeds its built maximum capacity of 350,000 passengers a day, with various solutions being proposed or implemented to alleviate chronic congestion in addition to the procurement of new rolling stock.

Since 2006, the system's private owners had been offering various capacity expansion proposals to the DOTC. In 2014, after the DOTC's handling of the line's maintenance for two years amid questions about the line's structural integrity owing to the poor maintenance and the pronouncements that the system, in general, was safe, experts from MTR HK were commissioned to review the system. MTR HK made the opinion that the rail system was compromised due to the DOTC's poor maintenance. In response to this, the line underwent a comprehensive rehabilitation program funded by Japan's official development assistance from 2019 to 2021. This resulted in upgraded facilities, railway tracks, trains, and other systems.

It is integrated with the public transit system in Metro Manila, and passengers also take various forms of road-based public transport, such as buses, to and from a station to reach their intended destination. Although the line is aimed at reducing traffic congestion and travel time along EDSA, the transportation system has only been partially successful due to the DOTC's inaction on the private sector's proposals to expand the capacity of the system to take up to 1.1 million passengers a day. Expanding the network's capacity to accommodate the rising number of passengers is currently set on tackling this problem.