Why do they call a parkway a parkway when you drve on it?

Answer 1

Ha.

The Straight Dope has an excellent explanation, as does Wikipedia's definition of Parkway.

From Wikipedia: Historically, the term "parkway" has often implied that the road was designed specifically with a naturalistic or manicured landscaping of the median and adjacent land areas meant to suggest a pastoral driving experience, isolated from the manifestations of commerce and advertising, even when the road passes through populated areas; for this reason commercial traffic is excluded. Many parkways have signature road signs with special emblems that suggest a thematic driving experience and increase the sense of isolation from civilization in the vicinity of the road.