“When do you go on red and stop on green?”/“When eating a watermelon.”

A popular children’s riddle is:
 
Q: When do you go on red and stop on green?
A: When you’re eating a watermelon.
 
The joke has been cited in print since at least 2001.
 
 
February 2001, Ranger Rick, “Reader riddles,” pg. 11:
When should you go on red and stop on green? When you’re eating a watermelon.
Grace C., Maryland
 
Google Books
Super Silly Riddles
By Charles Keller
Illustrated by Dave Winter
New York, NY: Sterling Publishing Company, Inc.
2002
Pg. 68:
When do you go on red and stop on green?
When you’re eating watermelon.
   
Google Books
March 2008, Boys’ Life, “Think & Grin,” pg. 56, col. 3:
Al: When do you go on red and stop on green?
Allison: When?
Al: When you’re eating a watermelon!
Robert Quebral, Williamsville, N.Y.
 
Twitter
Prongo kids games
‏@Prongo
Joke of the Day Submitted by: T:  Q.When do you go on red and stop on green? A.When you’re eating a watermelon! #LOL #Jokes
7:28 AM - 21 May 2009
   
Google Books
More One Liners, Jokes and Gags
By Grant Tucker
London: The Robson Press
2013
Pg. ?:
When do you go on red and stop on green?
When you’re eating a watermelon.
 
reddit—Shower Thoughts
When is the only time you “go” on red and “stop” on green?
submitted May 21, 2015 by vajeep
Watermelon.
 
reddit
When do you go on red and stop on green? (self.riddles)
submitted July 17, 2015 by kormer