With nearly one quarter of today's highway bridges rated as structurally deficient or functionally obsolete, it is ever more important to quantify the safe level of performance using in-situ structural health monitoring techniques. This paper discusses the experimental testing of a single simply supported span composite superstructure under various controlled progressive damage cases. The single span is part of a three span bridge located in northern New York. Using strain transducers mounted at the midspan and support locations, changes in load distribution factors and neutral axis locations are calculated to detect changes in load shedding behavior and structural capacity of the bridge span as diaphragm connections were severed and support conditions were altered to different levels. The results of the testing show that changes in the bridge response can be tracked as damage is introduced to the superstructure. The measurements are used to identify the diagnostic load testing parameters that can be used as structural health indicators that can in turn be used to complement current inspection protocols. Furthermore, the measurements also help provide a basis for future development of a performance index to be used in conjunction with existing condition rating measures for improved bridge condition assessment.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.