On classification by the newly formed Ministry of Transport in 1922, it formed parts of the A414 (Hatfield - St Albans), A412 (St Albans - Watford - Rickmansworth), A404 (Rickmansworth - Amersham), A416 (Amersham - High Wycombe - Marlow - Knowl Hill) and A32 (Marlow - Henley - Reading).