As its name suggests, the Baltimore-Washington Parkway is a 4-lane highway connecting Baltimore, Maryland and Washington, D.C. It is also known as MD Route 295.
It is also, however, a national park. This means that there are lots of trees on both sides of the road, a wide, woodsy median strip, and lovely stone guardrails. Additionally, no trucks are allowed. It also recieves federal funding, and is patrolled over more than half of its length (from MD route 175 - approximately Fort Meade- south to DC) by the National Park Police. Incidentally, this nationally-patrolled part is just about the shortest route from my parent's house (spitting distance of Fort Meade) to my school (University of Maryland, College Park).
The Parkway is 29 miles in length and passes through or near such august locations as Fort Meade and the National Security Agency, the Patuxent National Wildlife Refuge, the Beltsville Agricultural Research Center, Goddard Space Flight Center, the University of Maryland, and the National Arboretum. There are no tolls or fees for use of the Parkway, and as far as I know, no visitor center. Its fiscal year 2003 annual budget is $1,283,000. To all appearances, a good bit of this money will be spent on continuing the perpetual construction.
The original plan for the parkway was a part of Pierre Charles L'Enfant's original layout of Washington. The concept was approved a century later in 1902, at a time when "parkway" meant a road for bicycles and horse-drawn carriages. Construction, however, did not begin until 1942, at the end of the United States' parkway movement - making it one of the last parkways to be constructed nationwide, and one of two such in Maryland (the other is the Suitland Parkway). The Parkway opened in October 1954, with an average of 21000 vehicles traveling it in the first week. Judging by rush-hour traffic, I'd say the weekly average has gone way, way up in the intervening years, though I can't find any statistics to back that up.
In addition to "Baltimore-Washington Parkway" and "295", the road is also known as the Gladys Noon Spellman Parkway. Ms. Spellman was a Maryland congresswoman; the parkway was named for her in 1982 after she suffered a heart attack and languished comatose for the rest of her life. There was some controversy at the time about naming the highway for her; she was in no way involved with it, and many thought that in any case she would have preferred a more innocuous landfeature.
According to dem bones' list of U.S. National Parks and Monuments, the Baltimore-Washington Parkway is one of six similarly designated roadways in the nation, those others being the Blue Ridge Parkway, the George Washington Memorial Parkway, the John D. Rockefeller Jr. Memorial Parkway, the Natchez Trace Parkway, and the Suitland Parkway.
The National Scenic Byways Program site: http://www.byways.org/travel/byway.html?CX_BYWAY=2274&CX_STATE=MD
The National Park Services site: http://www.nps.gov/bawa/index.htm
And an editorial in the Baltimore Sun about Gladys Noon Spellman: http://www.sunspot.net/features/lifestyle/bal-to.memory09mar09.column?coll=bal-artslife-today