It runs from the A41 at a junction west of Hemel Hempstead in Hertfordshire, through the town to junction 8 of the M1 motorway at Buncefield, and running parallel to the M1 until junction 7, heading south of St Albans, east through Hatfield, Hertford, then across the A10 and into Essex through Harlow, Chipping Ongar and Chelmsford before terminating at Maldon.