The Metro Transit Police Department (MTPD) is the transit police agency of the Washington Metropolitan Area Transit Authority (WMATA), created by the WMATA Compact on June 4, 1976. The MTPD is unique in U.S. law enforcement as it is the only U.S. police agency that has full police authority in relation to a multi-state metro system. The MTPD has authority in three jurisdictions: Maryland, Virginia, and Washington, D.C. From Wikipedia