- A4251 between A41 / B4635 and Boswick Lane, Berkhamstead, Hertfordshire (Grid ref SP961100)
- A4251 between Boswick Lane and B4506, Hertfordshire (Grid ref SP970091)
- A4251 between B4506 and A416, Hertfordshire (Grid ref SP980084)
- A4251 between A416 and Hall Park Gate, Hertfordshire (Grid ref SP997075)
- A4251 between Hall Park Gate, Berkhamstead and A41, Hertfordshire (Grid ref TL008068)
- A4251 between A41 and B4505, Hertfordshire (Grid ref TL034059)
- A4251 between B4505 and A4146, Hertfordshire (Grid ref TL045060)
- A4251 between A4146 and A414, Hertfordshire (Grid ref TL050058)
- A4251 between A414 and Nash Mills Lane, Hertfordshire (Grid ref TL061050)
- A4251 between Nash Mills Lane, Hemel Hempstead and Home Park Mill Link Rd, Kings Langley, Hertfordshire (Grid ref TL074020)
- A4251 between Home Park Mill Link Rd, Kings Langley and M25 Jn20, Hertfordshire (Grid ref TL075017)