No way to go through a congested area (6)
I believe the answer is:
bypass
'a congested area' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'no way to go' is the wordplay.
'no way' becomes 'by' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to go' becomes 'pass' (synonyms).
'by'+'pass'='BYPASS'
'through' acts as a link.
Can you help me to learn more?
(Other definitions for bypass that I've seen before include "Way to avoid town etc" , "Circumvent" , "Go round (congested area etc)" , "Sort of surgery" , "heart operation" .)