As you come from Thorpe Wood (A) and attempt to take the 3rd exit onto the A47 to Wisbech (C), the first part of joining the roundabout is to be aware that cars come very fast off the Nene Parkway from your right. As you enter the roundabout you commonly have to slow down as there is usually traffic queuing up to the traffic lights at point (B).

This clip is joining the Thorpe Wood roundabout from the Thorpe Wood exit and going round the roundabout once and then joining the A47 in the direction of Wisbech: