This paper focuses on the calculation of load and resistance factors for the first edition of the OHBDC, following a specially developed reliability-based calibration procedure. It involved the selection of representative bridges, the formulation of limit state functions, the development of reliability analysis procedure, the development of statistical parameters for load and resistance, the reliability analysis for representative bridges, the selection of the target reliability index, and lastly the determination of load and resistance factors. This was one of the first applications of newly developed reliability analysis procedures. The required statistical parameters of load components were determined from very limited measurements and mostly using engineering judgment (Delphi method), relying on an expert opinion. Live load parameters were based on the results of the truck survey in Ontario in 1978. Dynamic load was first based on field measurements and then modified based on dynamic analysis. Many of these early statistics are still unquestioned. The statistical parameters of resistance were based on the available literature, research reports, and material test results. These statistics were later updated. Many of the original recommendations still remain unquestioned.