Where traffic is moving from place to place (2,3,4)
I believe the answer is:
on the road
'where traffic' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'moving from place to place' is the wordplay.
I cannot quite understand how this works, but
'moving' could be 'road' ('road' can be similar in meaning to 'moving') and 'road' is found within the answer.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for on the road that I've seen before include "Jack Kerouac novel" , "accompanying The Travelling People?" , "way to travel" , "Travelling (like Jack Kerouac?)" , "as a commercial traveller?" .)