Senior Guide’s bit of road rage (6)
I believe the answer is:
ranger
'senior guide's' is the definition.
(Rangers is an older Girl Guiding group)
'bit of road rage' is the wordplay.
'bit of' indicates taking the first letters.
'rage' becomes 'anger' (I've seen this before).
The initial letter of 'road' is 'r'.
'r'+'anger'='RANGER'
(Other definitions for ranger that I've seen before include "Park/forest keeper" , "Forest defender" , "Keeper of national park or Texas policeman" , "Park employee" , "Forestry official" .)