Alabang Viaduct
Carries	AH 26 (E2) (South Luzon Expressway)
Crosses	Manila South Road (Alabang–Zapote Road / Montillano Street)
Locale	Alabang, Muntinlupa, Metro Manila, Philippines
Official name	Alabang Viaduct
Maintained by	SMC SLEX, Inc. / Manila Toll Expressway Systems (MATES)
Characteristics
Design	Viaduct (Prestressed concrete girder bridge)
Material	Prestressed concrete
Total length	1.2 kilometers (0.7 mi)
No. of lanes	8 lanes (4 lanes northbound, 4 lanes southbound)
History
Engineering design by	Katahira & Engineers International (rehabilitation and widening)
Constructed by	F.F. Cruz & Co. (rehabilitation and widening)
Opened	May 4, 1978; 48 years ago (1978-05-04)
Statistics
Toll	See SLEX toll matrix

The Alabang Viaduct is a 1.2-kilometer (0.7 mi)-long, elevated highway viaduct in Muntinlupa, Metro Manila, Philippines. It carries the primary traffic flow of the South Luzon Expressway (SLEX) over the highly congested junction of the Manila South Road, Alabang–Zapote Road, and Montillano Street.

Constructed in the late 1970s to extend the expressway further south into the Calabarzon region, the viaduct underwent a massive structural overhaul and engineering redesign between 2006 and 2008 to expand its capacity.

The Alabang Viaduct was conceptualized as a critical component of the Manila South Expressway Extension project, which extended the original 15-kilometer (9.3 mi) highway south from Alabang into the provinces of Laguna and Cavite. Construction began in 1976 under the main general contractor, the Construction Development Corporation of the Philippines (CDCP), which was later reorganized as the Philippine National Construction Corporation (PNCC).^[1]

The completed extension, which prominently featured the elevated structure over the Alabang junction, was formally completed and inaugurated on May 4, 1978.^[2][3] Upon its public opening, the structural core spanned an initial footprint of 840 meters (2,760 ft) and carried six traffic lanes, making it the longest highway viaduct of its class in the country at the time.^[1]

When opened in 1978, the initial viaduct structure was engineered and built utilizing a specialized prestressed concrete Super-T girder configuration.^{[citation needed]} This layout was implemented during the initial late-1970s extension push by the CDCP to provide long spans over the heavy right-of-way constraints of the Alabang intersection below.^[4]

By the early 2000s, structural degradation due to excessive vehicular loads and severe traffic congestion prompted the local government to call for emergency structural reviews.^[5] In February 2006, the Supplemental Toll Operation Agreement (STOA) was authorized, tasking the South Luzon Tollway Corporation (SLTC) to initiate the SLEX Rehabilitation and Widening Project, where the retrofitting of the Alabang Viaduct was formally designated as Toll Road 1 (TR-1).^[6][7]

The Japanese civil engineering consulting firm Katahira & Engineers International (KEI) served as the lead designer for the modern structural overhaul.^[8] Under Katahira's engineering design, the original superstructure was completely converted to standard AASHTO girder design standards.^{[citation needed]} Local contractor F.F. Cruz & Co. was tapped to undertake a structural rehabilitation work.^[9] The choice of standardized precast AASHTO beams allowed engineers to successfully widen the viaduct deck from six lanes to eight lanes to accommodate modern high-volume expressway capacity without altering the physical baseline footprint of the original concrete piers underneath.^{[citation needed]} The rehabilitation and widening of the viaduct was completed on December 11, 2008.^[10]

Despite the 2008 widening, the viaduct remained a major traffic bottleneck for motorists transitioning between the standard expressway and the Skyway System. In 2019, San Miguel Corporation launched the SLEX Elevated Extension Project, constructing a multi-kilometer elevated bypass system that runs parallel to and above the Alabang Viaduct, allowing long-distance commuter traffic to bypass the Alabang bottleneck entirely.^[11]

• South Luzon Expressway
• Metro Manila Skyway
• List of bridges in the Philippines