Area in which to turn a car during a race (5)
I believe the answer is:
tract
'area' is the definition.
(tract is a kind of area)
'to turn a car during a race' is the wordplay.
'to turn' is a reversal indicator.
'during' means one lot of letters goes inside another.
'a race' becomes 'tt'.
'car' inserted into 'tt' is 'tcart'.
'tcart' in reverse letter order is 'TRACT'.
'in which' is the link.
(Other definitions for tract that I've seen before include "Printed leaflet" , "Large area of land or small booklet" , "religious work, often" , "Large area; treatise" , "Anatomical structure" .)