South Sudan has an estimated rural bridge deficit of 680 crossings below 25 m span, representing the primary physical barrier to year-round agricultural market access, emergency humanitarian logistics, and community healthcare connectivity for approximately 4.2 million rural inhabitants. Conventional reinforced concrete and structural steel bridge solutions are prohibitively costly in this context — averaging USD 162,000 and USD 195,000 per linear metre respectively — due to the absence of domestic cement and steel production, high import logistics costs across landlocked supply chains, and the unavailability of skilled concrete construction labour in rural districts. Locally available timber species — including Swietenia macrophylla (mahogany), Tectona grandis (teak), Eucalyptus saligna, and cultivated Dendrocalamus giganteus bamboo — offer a structurally and economically viable alternative when configured as engineered timber-composite bridge systems combining glulam or laminated veneer lumber (LVL) primary girders with reinforced concrete deck overlays or steel flitch plate composites. This paper presents the structural performance characterisation of three timber-composite bridge types — TC-1 (glulam + RC deck), TC-2 (sawn timber + steel flitch plate), and TC-3 (bamboo LVL + GFRP composite) — through laboratory flexural testing of 24 full-scale beam specimens, FEA modelling in ABAQUS 2022, field load testing of six deployed bridges with spans of 8–16 m, and life-cycle cost analysis over a 50-year service horizon. TC-1 achieves an effective flexural stiffness of EI_eff = 6.85×10¹⁰ N·mm², a design moment resistance of M_Rd = 42.2 kN·m, and a self-weight ratio of 2.4 relative to an equivalent RC T-beam — enabling deployment by community labour with locally hired motori