Police on radio evacuated transit network (5)
I believe the answer is:
metro
'transit network' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'police on radio evacuated' is the wordplay.
'police' becomes 'met' (London Metropolitan Police).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'evacuated' suggests removing the centre (internal letters are evacuated from the word).
'radio' with its centre taken out is 'ro'.
'met'+'ro'='METRO'
Can you help me to learn more?
(Other definitions for metro that I've seen before include "French underground" , "Parisian underground railway" , "what moves many Parisians" , "The underground railway system in Paris" , "Parisian underground system" .)