If you are planning to travel to Knockalls via Chepstow and the B4228 to Coleford, you should allow an extra 10-15 minutes to follow the diversion around Coleford centre caused by a road closure at the main traffic lights by the town centre.
Remember that access to the forest from the Chepstow – Redbook – Newland Road is very restricted, so if travelling from Chepstow to Knockalls the best option currently seems to be the A466 to Monmouth, and then the A4136 towards Coleford, turning off it in Staunton village.