[not a teacher]
Some examples as idioms:
"on the road" - traveling away from home, touring
eg. The circus took their show on the road.
"on the street" - (as in "the word on the street") unofficial, hidden, illicit
eg. I heard on the street that that U2's new CD is terrible!
"in the street" is not idiomatic, but it is common, as in, "Quit playing in the street, you'll get hit by a car!"
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