A proof-load test is often necessary to accurately measure the field behavior of a bridge structure. A new segmental steel bridge has been constructed over the Tisza River in Hungary. The bridge comprises of two independent steel box girders assembled by a welding system. Engineers performed proof load tests before opening the structure to evaluate its load-carrying capacity and deck deflection. This paper presents several aspects of the load testing and evaluation of the bridge structure under static and dynamic loads using a rating factor (RF) approach compared to a baseline finite element model. The load test results helped to calibrate the model and verify the method. The study reveals that the tested bridge has an elastic behavior, a high capacity, and adequate dynamic performance.