Whenever under the appropriations made by Congress, the roadway of any street, avenue, or road in the District of Columbia is paved or repaved with sheet asphalt, asphalt block, asphaltic or bituminous concrete (except penetration macadam), cement concrete, granite block, vitrified brick, or other form of permanent pavement, one-half of the total cost thereof shall be charged against and become a lien upon the abutting property, and assessments therefor shall be levied pro rata according to the linear frontage of said property on the street, avenue, or road, or portion thereof, upon the roadway of which said new pavement or repaving is laid; provided, however, that when such new pavement or repaving is laid solely on 1 side of the centerline of such roadway, the one-half cost thereof shall be assessed, as herein provided, against the property abutting the side of the street, avenue, or road, or portion thereof, so improved.

For the purposes of computing the assessments under this subchapter, the term "roadway" shall be construed to include the gutters and curbings; provided, however, that where any permanent and new construction of curb, or curb and gutter, is laid, and the roadway of the street is not paved or repaved, or is not paved or repaved with a pavement of the character specified in § 9- 421.01, the half cost of such curb, or curb and gutter, shall be assessed against the abutting property in the manner provided in this subchapter.

There shall be excepted from such assessments the cost of paving the roadway in excess of 40 feet in width where the new pavement or repaving is laid on both sides of the centerline of such roadway; the cost of paving the roadway in excess of 20 feet in width where the new pavement or repaving is laid solely on 1 side of the centerline of such roadway; the cost of paving the roadway space included within the intersection of streets, avenues, and roads, as said intersections are limited by lines normally projected from the building lines of the street, avenue, or road being improved at its point of intersection with the building lines of the intersecting streets, avenues, or roads and also the cost of paving or repaving the space within such roadways for which street railway companies are responsible under their charters or under law, on streets, avenues, or roads where such railways have been or shall be constructed.

The maximum linear front foot assessment levied hereunder shall not exceed $3.50 per linear front foot. The total assessment levied hereunder against any abutting property shall not exceed the number of square feet of area of said property multiplied by 1 per centum of the linear front-foot assessment, and shall not exceed 20 per centum of the value of the said abutting property, exclusive of improvements thereon, as assessed for the purpose of taxation at the time of the paving or repairing of the street, avenue, or road for which said assessment is levied. In computing assessments hereunder against unsubdivided land by the square foot or according to the assessed valuation, there shall be excluded from the computation land lying back more than 100 feet from the street, avenue, or road being improved where the depth is even; where the depth is uneven, the average depth shall be taken in computation, but not to exceed 100 feet.

No property on which a legal assessment has been levied and paid for paving or repaving, curbing or curbing and guttering, on the roadway of any street, avenue, or road, shall be liable for any further assessment under this subchapter on account of the replacement of such pavement, curbing, or curbing and guttering.

No assessments shall be levied for repaving where the original pavement was laid at the whole cost of the owner or owners of the abutting property if the said original pavement was constructed under a permit issued by the District of Columbia and under the supervision and direction of an authorized engineer and inspector of the Department of Transportation of said District, in strict accordance with the then current specifications and design for pavements of the type for which permit was issued; provided, that where curb, or curb and gutter, or a part of the roadway has or have been paved under proper permit, subject to engineering and inspection as above stated, the assessment for paving other parts of the roadway, placing curb, or curb and gutter, when the same is done at public expense, shall be made against property abutting on the highway as provided in this subchapter, credit being given in such assessment for the half cost of the pavement laid by the owner under permit as above, estimated on the basis of the contract rates for such work at the date of the performance of the assessable work, so that the total cost to the owner for such improvements shall not exceed the amount of assessments which would have been made under this subchapter, had the improvements been all made at public expense.

No assessment shall be levied for the cost of resurfacing asphalt pavements by the heater method -- stripping the surface from a rigid type base, and replacing surface thereon -- or covering an existing hard surface or macadam pavement or base with bituminous material; provided, that where an entire pavement is removed and replaced with a pavement of the character specified in § 9-421.01, the cost of the latter pavement shall be assessed as provided in this subchapter, if no previous legal assessment has been levied and paid therefor.

When any property abuts 2 or more streets, avenues, or roads, the assessments against said property levied under this subchapter shall not exceed in the aggregate, together with any legal assessments levied and paid prior to February 20, 1931, for the paving, curbing, or curbing and guttering of or on said streets, avenues, or roads, 3 1/2 cents per square foot of area of said property, or 20 per centum of the value of said property, exclusive of improvements thereon, as assessed for purposes of taxation at the time of the paving or repaving, curbing, or curbing and guttering for which the assessment is levied.

The assessments provided for in §§ 9-421.01 to 9-421.12 shall be made and collected as provided in § 9-401.06, relating to alleys and sidewalks.   The rate of interest to be charged upon any assessment, levied under § 9-401.06 relating to alleys and sidewalks, or any instalment thereof, is reduced hereby from 8 per centum per annum to 6 per centum per annum; provided, however, that any instalment of any such assessment not paid within the time provided in § 9-401.06 shall thereafter bear interest at the rate of 12 per centum per annum; and provided further, that the advertisement by publication of the intention of the Mayor of the District of Columbia to perform the work and the formal hearing in respect thereto required by law as to alley and sidewalk improvements shall not be required as to roadway, curbing, and gutter improvements.

Any property owner, aggrieved by any assessment levied under this subchapter, may, within 60 days after service of notice of such assessment, file with the Mayor of the District of Columbia a protest in writing against such assessment, accompanied by affidavits if he so desires, and if said Mayor finds that the property of such owner so protesting is not benefited by the improvement for which said assessment is levied, or is benefited less than the amount of such assessment, or is unequally or inequitably assessed with relation to other property abutting such improvement, said Mayor shall abate, reduce, or adjust such assessment in accordance with such finding.   In computing the 60 days provided in § 9-401.06, within which such assessment may be paid without interest, there shall be excluded therefrom the time between the date of the filing of any such protest and the date of action thereon by the Mayor.

The Mayor of the District of Columbia is directed to cancel all assessments for improvements completed within 3 years prior to February 20, 1931, levied under the authority of this subchapter, relating to assessments for the paving of streets, avenues, and roads, or under § 9-401.04, relating to assessments for laying curbs; and the Mayor is further directed to reassess the cost of such improvements against the abutting property in accordance with the provisions of this subchapter, which assessments shall become a lien upon the abutting property and be collected in the manner provided under this subchapter. Where assessments for such improvements have been paid in whole or in part the Mayor shall refund, within the limits of appropriations by Congress therefor, to the persons paying the same, the excess, if any, of such payments over the amounts of the reassessments levied under §§ 9-421.01 to 9- 421.12.

Should any provision of this subchapter be decided by the courts to be unconstitutional or invalid, the validity of §§ 9-421.01 to 9-421.12 as a whole or of any part thereof other than the part decided to be unconstitutional shall not be affected.