The numbering plan area (NPA) comprises the western part of the state, including Maryland's portion of the Greater Washington, D.C. metro area and portions of southern Maryland. This includes the communities of Cumberland, Frederick, Hagerstown, Gaithersburg, Potomac, Bethesda, Rockville, Landover and Silver Spring. Area code 301 was one of the original area codes established in 1947 when the NANP was created. Its original numbering plan area comprised the entire state of Maryland. From 1947 to 1990, the telephone numbering plan of the entire Washington metropolitan area, including Washington, D.C. (area code 202), and the large suburban areas in Maryland and Virginia (area code 703), operated in a system of central office code protection, meaning that no central office code in Washington D.C., and in the Maryland and Virginia suburbs could exist in more than a single central office. As a result, it was possible for telephone users in the metropolitan area to dial any other telephone number in the area as a local call with only seven digits, without using an area code. The entire metro area was reachable via long-distance services by dialing area code 202, for which purpose AT&T had established cross-referenced operator routing codes for all affected central offices. For example, if 202-574 numbers were in use in the district or 703-574 numbers were in use in Northern Virginia, the corresponding 301-574 numbering block could only be assigned in areas considered a safe distance away from the capital, such as the Eastern Shore of Maryland. By the end of the 1980s, the Washington metropolitan area was running out of prefixes. This code exhaustion was mitigated on October 1, 1990, by removing code protection in 202. As of that date, all local metro area calls between Maryland, the District of Columbia, and Virginia required dialing the area code for calls to another NPA. Area code 202 was no longer useable for suburban points. Local calls within Maryland did not require the area code. Despite the overall growth of the Baltimore–Washington metropolitan area, 301 remained the exclusive area code for Maryland for 44 years, making Maryland one of the largest states with a single area code. By the end of the 1980s, however, it became apparent that breaking seven-digit dialing in the Washington area would not free up enough numbers to stave off the need for a new area code. Baltimore and the Eastern Shore were split off as a new numbering plan area with area code 410 on October 6, 1991.