Two 21km long viaducts built along existing S.Y.S. Freeway which is heavily congested at all times.  To accommodate local environment and maintain traffic flow, various types of superstructures have been contemplated and designed including P.C. I-girders, steel box girders, cantilever P.C. box girders, C.I.P. double T girders; substructures are single column type with variable or constant cross sections.  Foundation types include reverse circulation piles, C.I.P concrete piles with full casing , and R.C. caissons.