The recent completion of a California Department of Transportation construction evaluated precast thin wall reinforced concrete (semicircular) arch at San Martinez Grande affirmed the application of the dimension ratio design concept to reinforced concrete semicircular arch design. The recent culvert research was further supported by the complete and comprehensive California Department of Transportation reinforced concrete arch culvert research previously reported at Posey Canyon and Cedar Creek. The observed vertical and horizontal pressures observed at Posey Canyon and Cedar Creek are consistent with the application of the dimension ratio concept to reinforced concrete arch design. A significant reduction can be made in the wall thickness of reinforced concrete semicircular arch designs, resulting in substantial future savings.