The story
Coined by City Housing Corporation for Radburn c. 1928, according to Stuart Chase in The New York Times, June 24, 1928. Ostensibly from rad (“quick”) + burn (“brook”). The brook being referenced is Saddle River, according to Radburn's landscape architect Marjorie Sewell Cautley. 1930, Marjorie Sewell Cautley, “Planting At Radburn”, in Landscape Architecture Magazine, volume 21, number 1, page 26: Along the Saddle River the problem will be a simple one of preserving old trees and water plants. In this stream for which "Rad Burn" is named, boys have fished and waded since the days when slaves chanted spirituals in the tiny chapel on the Dunkerhook farm.
Etymology from Wiktionary, CC BY-SA 4.0.