Effects of horizontal splitter plates on the vortex-induced vibration and aerostatic characteristics of twin separated parallel decks for a rail-cum-road bridge

• Incoming flow direction significantly influences the VIV response and aerostatic coefficients of twin parallel decks. • Splitter plates suppress vortex generation, shedding, and impingement, reducing fluctuating pressure and effectively mitigating VIV. • The highway deck exhibits both vertical and torsional VIV, while the railway deck only shows vertical VIV when upstream. • Splitter plates compromise static wind stability of the upstream deck but have minimal effect on the downstream deck, warranting optimal width selection.