The resistance of a section of roadway in which there is a pressure of 1 lb/ft₂(6.9 kPa) throughout the section, when an amount of 1,000 ft₃/s (1 kilocusec or 28.3 m₃/s) of dry air at 60 degrees F (15.6 degrees C) and 30 in (762 mm) barometer is passing.