Minimum street grades of 0.6 percent will be required with the maximum grade being seven (7) percent for collector streets and ten (10) percent for minor streets. Where the observance of this standard is unfeasible, the Planning Commission shall have the power to grant an exception when special pavement surfaces and adequate leveling areas are installed or in the opinion of the Planning Commission the best subdivision of the land is thereby secured. (PZSC § 03-28-005 (2) (E))