Abstract: A precast segmental viaduct construction system, comprises an elongated erection and assembly vehicle for spanning between at least two viaduct piers and for moving between successive piers, the vehicle having a top deck, an elongated central longitudinal beam having a down facing elongated planar bottom support surface, a pair of elongated trusses secured to and inclined outward from said beam, and a pair of elongated longitudinal planar top support surfaces extending along opposite side edges of said top deck, a plurality of jacks spaced along the vehicle for cooperatively engaging piers on which the vehicle is supported for positioning the vehicle relative to piers on which it is supported, and a support assembly for supporting the vehicle on a pier, the support assembly having jacks for selectively elevating and lowering the vehicle.