What does the poem Traffic Light by Shel Silverstein mean?

Take Ten (1955)

Grab Your Socks!(1956)

Report From Practically Nowhere (1960)

Uncle Shelby's ABZ Book (1961)

Lafcadio, the Lion Who Shot Back (1963)

A Playboy's Teevie Jeebies (1963)

A Giraffe and a Half (1964)

The Giving Tree (1964)

Who Wants a Cheap Rhinoceros? (1964, revised in 1983)

Uncle Shelby's Zoo: Don't Bump the Glump! (1964)

More Playboy's Teevie Jeebies: Do-It-Yourself Dialogue for the Late Late Show (1965)

Where the Sidewalk Ends (1974)

The Missing Piece (1976)

Different Dances (1979)

A Light in the Attic (1981)

The Missing Piece Meets the Big O (1981)

Falling Up (1996)