A 50-year-old bridge showed large cracking in the approach bridge parts due to restraint of deformation and support settlement. After repair, it was uncertain at which crack width the traffic loads on the bridge should be further restricted. The shear capacity was calculated by counting on the aggregate interlock capacity of a supposedly fully cracked cross-section. An aggregate interlock relation between shear capacity and crack width based on an unreinforced section was used to find the crack width at which the shear capacity of the section with a through crack becomes smaller than the shear capacity of the section without a through crack. Limits for crack widths at which load restrictions should be imposed were found. The large structural capacity of the cracked concrete section shows that the residual bearing resistance based on the aggregate interlock capacity of reinforced concrete slab bridges with existing cracks is higher than expected.