EPA is approving State Implementation Plan (SIP) revisions submitted by the State of Maryland on December 20, 2007, November 12, 2010, and June 22, 2011, as amended March 22, 2013. These SIP revisions pertain to adoption by Maryland of a Low Emission Vehicle (LEV) program, which incorporates by reference California's second generation Low Emission Vehicle (LEVII) program regulations. Maryland's LEV regulations require new 2011 and subsequent model year passenger cars, light trucks, and medium-duty vehicles having a gross vehicle weight rating (GVWR) of 14,000 pounds or less that are sold in Maryland to meet California emission standards. The Clean Air Act (CAA) contains authority by which states other than California may adopt new motor vehicle emissions standards that are identical to California's standards. Maryland's supplemental SIP revisions submitted on November 12, 2010 and June 22, 2011 modify its program to harmonize with updates by California to its LEVII program and Federal GHG standards effective on 2012-2016 model year vehicles. The March 22, 2013 SIP amendment withdraws from the SIP revision submittal the portion of Maryland's LEV program rule that incorporates by reference a provision of California's rule regulating retrofit systems for conversion of motor vehicles to use natural gas or liquefied petroleum gas in lieu of the fuel on which they were originally certified. EPA is approving all of Maryland's LEV Program SIP revisions, except for the portion of Maryland's regulation withdrawn by Maryland from the SIP on March 22, 2013, in accordance with the requirements of the CAA.