Abstract: In this paper, a parametric study that investigated geometrical parameters of reinforced concrete box culverts (RCBC) is presented. Dead and live loads, which act on RCBC, and derivation of vehicle load formulas were explained. These formulas were verified by comparison with experimental studies. Span width, culvert height and fill depth effects on RCBC design were investigated by creating a number of 88 2D finite element culvert models. An Excel sheet was developed by using VBA and CSI API to establish SAP2000 models and to generate analysis results. Analysis results revealed that while vehicle load was predominant for fills that did not have a depth value greater than 1 m, vertical earth load was predominant beyond this value. Minimum values of internal forces and base soil pressures occurred at 0.7–1.0 m fill depth range. It is concluded that span width and fill depth parameters have an important effect on internal forces of RCBC models. This research also reveals that using multiple cell RCBC instead of using wider span width in single cell RCBC is more reliable due to much lower internal forces and base soil stresses.