Nice road held up when on A1 northbound - a lot of people live here (7)
I believe the answer is:
eurasia
'a1 northbound a lot of people live here' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'nice road held up when on' is the wordplay.
'nice' becomes 'eur' (I am not sure about this - if you are sure you should believe this answer much more).
'road' becomes 'AI' (resembles Ae, a major UK road).
'held up' says the letters should be written in reverse.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'on' means one lot of letters go next to another.
'ai' back-to-front is 'ia'.
'ia' put after 'as' is 'asia'.
'eur'+'asia'='EURASIA'
Can you help me to learn more?
(Other definitions for eurasia that I've seen before include "large bloc of countries" , "Huge area" , "Landmass extending from Cape Roca in the west to Cape Dezhnev in the east" , "Supercontinent" , "World's largest land mass" .)