Arlington County, Virginia was linked to the system on July 1, 1977; Montgomery County, Maryland, on February 6, 1978; Prince George's County, Maryland, on November 17, 1978; and Fairfax County, Virginia, and Alexandria, Virginia, on December 17, 1983.
Arlington County, Virginia 1 Temmuz 1977'de; Montgomery County, Maryland, 6 Şubat 1978'de; Prince George's County, Maryland, 20 Kasım 1978'de; ve Fairfax County, Virginia, ile Alexandria, Virginia, 17 Aralık 1983'te sisteme bağlandı.