Special assessments for curbs and gutters levied.

When any curb or gutter is laid, or any curb and gutter are laid, on any street, avenue, or road in the District of Columbia which said curb shall be constructed of concrete, stone, or other permanent type of construction, or which said gutter shall be constructed of concrete, brick, granite block, asphalt on a concrete base, or other permanent type of construction, one-half of the total cost thereof shall be charged against and become a lien upon the property abutting the side of the street, avenue, or road, or portion thereof, so improved, and assessments therefor shall be levied pro rata according to the linear frontage of said property on the side of the street, avenue, or road, or portion thereof, so improved; provided, however, that no assessments shall be levied hereunder on account of the replacement of any curb or gutter or curb and gutter of a permanent type of construction. When any gutter shall be constructed, in whole or in part, as an integral portion of a permanent type of roadway of any street, avenue, or road, so much of said roadway as lies within 2 feet of the curb line shall be considered as a gutter for the purposes of this subchapter.