Pennsylvania Avenue lighthearted celebrations, including a series of day- and nighttime Shriner's parades in the 1920s and 1930s. Thomas and Concepcion Picciotto are the founders of the White House Peace Vigil, the longest running anti-nuclear peace vigil in the US, at Lafayette Square on the 1600 block of Pennsylvania Avenue. After the Oklahoma City bombing in 1995, the Secret Service closed the portion of Pennsylvania Avenue in front of the White House to all vehicular traffic. Pedestrian and bicycle traffic, however, was still permitted on the sidewalk. After 9/11 this policy was made permanent. Near the White House traffic is redirected to
White House II in order to hide the construction of an underground bunker to be used in emergencies. The bunker has come to be known as the Presidential Emergency Operations Center. The White House and grounds cover just over 18 acres (about 7.3 hectares). Before the construction of the North Portico, most public events were entered from the South Lawn, which was graded and planted by Thomas Jefferson. Jefferson also drafted a planting plan for the North Lawn that included large trees that would have mostly obscured the house from Pennsylvania Avenue. During the mid-to-late 19th century a series of ever larger