A lack of cars, usually, approaching a built-up area (8)
I believe the answer is:
scarcity
'a lack' is the definition.
(thesaurus)
'up area' is the wordplay.
'up' becomes 'scar' (I am not sure about this - if you are sure you should believe this answer much more).
'area' becomes 'city' (city is a kind of area).
'scar'+'city'='SCARCITY'
'of cars usually approaching a built' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for scarcity that I've seen before include "Shortness of supply" , "Something uncommon" , "Inadequate supply" , "Thinness" , "Shortage" .)