DescriptionDeflection and vibration significantly impact the serviceability of bridges. Deflection limits are based on subjective human responses that are not directly related to a bridge's structural integrity or vibration control. Nonetheless, deflection limits are indirectly used to limit bridge vibrations. Over the years, significant changes have occurred in the field of bridge design and construction. Today's bridges are designed with longer spans, stronger materials, and lighter decks, which impact how the bridges respond under different live loads. Five existing bridges will be used to investigate the relationship between deflection and vibration. Each bridge will be modeled using the grillage method and remodeled with adjustments made to the thickness of the deck, concrete density of the deck, and girder size. Lastly, the vibration parameters of the existing bridges and the modified bridges will be compared with current design limits and criteria.