Herdsman went by car to the top of the road (6)
I believe the answer is:
drover
'herdsman' is the definition.
(I know that herdsman can be written as drover)
'went by car to the top of the road' is the wordplay.
'went by car' becomes 'drove' (I've seen this before).
'to the top of' suggests taking the first letters.
The initial letter of 'road' is 'r'.
'drove'+'r'='DROVER'
(Other definitions for drover that I've seen before include "One moving a herd or flock" , "Herder of cattle" , "One driving cattle" , "One driving flock to market" , "Cattle hand" .)