Span the canyon on a budget. Your design is solved with a real stiffness-method finite element analysis (two planar girders, frame deck, tension-only cables, Euler buckling) and then tested by moving vehicles. Overstressed members fail and the structure collapses into the river.
Model: each of the two girders is a plane frame solved with the direct stiffness method (dense Cholesky). Steel/wood/cable members are pin-jointed bars, the concrete deck is a beam-column. Cables carry tension only (iterated). Compression is limited by min(yield, Euler pi^2 EI / L^2). Vehicle axle loads are moved along the deck with a 1.2 impact factor; the wind term is the in-plane component plus deck uplift; earthquake is equivalent-static horizontal + vertical inertial load.