The Candaba Viaduct (also known as Pulilan–Apalit Bridge) is a 5-kilometer (3.1 mi) viaduct carrying the North Luzon Expressway (NLEX) across swampland in Candaba, Pampanga. Consisting of four lanes (two northbound and two southbound), it is the longest bridge in the Philippines. The viaduct was designed by Aas-Jakobsen and built by Construction Development Corporation of the Philippines (CDCP, later renamed to Philippine National Construction Corporation) as part of construction of the whole NLEX.
Built in 1976, the bridge and the whole stretch of NLEX were constructed as a component project of the International Bank for Reconstruction and Development through the direction of the Ministry of Public Highways. The project was completed in 1977 and through Presidential Decree 1113, then President Ferdinand Marcos granted CDCP the franchise to maintain and operate the NLEX including the Candaba Viaduct. On February 10, 2005, the operations and maintenance of the whole of NLEX were transferred to the Manila North Tollways Corporation.
Overlooking Mount Arayat, the viaduct is raised over Candaba Swamp, which keeps the highway open to traffic, even when the swamp gets flooded during the rainy or monsoon season. Lighting, emergency callboxes and CCTVs along the viaduct are powered by solar panels due to the problem of installing power lines within the viaduct.
In February 2017, it was announced that Candaba Viaduct will be expanded and will have a third lanes on both sides of the bridge.
The Candaba Viaduct passes over Candaba Swamp and adjacent Pampanga River and connects the provinces of Pampanga and Bulacan, hence its alternative name. Most of its portions are lined with billboards, ricefields, and some trees. The Hermosa-Duhat-Balintawak transmission line of National Grid Corporation of the Philippines (NGCP) utilizes the western side of the viaduct since March 2011 as the line is relocated due to the widening of MacArthur Highway, where the steel poles posed a safety hazard.
The viaduct starts at Barangay Dulong Malabon in Pulilan where there are a few houses located under it and after a few meters, it enters the municipality of Calumpit. It enters Pampanga (Apalit) after passing an area with palm trees, continues a straight route, and passes through Pampanga River, where its parish church is visible from the road. A footbridge is located on its southbound lane. The bridge ends after crossing Pampanga River.