Md. Code, Courts and Judicial Proceedings § 10-312

(a) Subject to subsection (b) of this section, in a prosecution for a diesel emissions standard violation under Title 23, Subtitle 4 of the Transportation Article, emissions test results from emissions test equipment as described in § 23-402 of the Transportation Article are admissible at trial in any court with jurisdiction over the proceeding in the State.

(b) If at the time of testing, a diesel vehicle fails to meet the emissions standard established under Title 23, Subtitle 4 of the Transportation Article, the failure to meet the established emissions standard shall be prima facie evidence that the operator of the diesel vehicle violated the provisions of Title 23, Subtitle 4 of the Transportation Article.