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This paper presents the results of a parametric study of load distribution in 108 four-sided precast concrete box culverts using three-dimensional finite element analysis (FEA) and two-dimensional plane frame analysis. Three concrete box culvert sizes were chosen with various span lengths, constant rise, and standard laying width. The culverts are subjected to various combinations of earth loading from the soil cover, lateral earth pressure, and AASHTO HS20 wheel loading applied at centre or edge along midspan of the top slab. As the soil cover increases from 0 to 3 m (10 ft), wheel loads are projected to the top slab using ASTM C890 procedure. Maximum bending moments and deflections were computed and evaluated. As expected, the study showed that the effect of wheel loading along midspan is significant and that the edge loading condition for a single box is more critical than centre loading for soil cover less than 0.9 m (3 ft). The earth loading tends to gradually dominate as the soil cover increases, which is expected based on geotechnical engineering practices. The effect of wheel loading position along midspan (edge vs centre) for soil cover greater than 2.1 m (7 ft) is negligible. It was shown that the plane frame analysis and 3D FEA gave similar results for long-span culverts. However, for short-span (3.6 m or 12 ft) concrete box culverts, the plane frame analysis was less conservative than the 3D FEA by about 15% and 25% for moments and deflections, respectively; versus about 5% and 10% for the long-span culvert (7.2 m or 24 ft) considered.