D.C. Code § 9-421.08

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, 31/2 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.