There have been significant advances in development of high performance materials over the past two decades, such as high performance steel (HPS). HPS offers higher yield strength, enhanced weldability, and improved toughness, which results in smaller cross sections, lighter and much more economical designs. On the other hand, smaller cross section leads to more flexible bridges that do not satisfy the existing serviceability deflection criteria. AASHTO Standard Specifications limit live load service deflection to L/800 for general bridges and to L/1000 for bridges that are used by pedestrians. These limits were employed to avoid "undesirable structural and psychological effects due to their deformations." However, results of prior studies indicate that deflection and L/D limits do not necessarily address these objectives. Human susceptibility is more influenced by derivatives of deflection rather than the deflection itself. Thus, there is a need for development of a more rational serviceability criterion, which is the objective of this study and some preliminary results are presented in this paper.