We used to live in the area (Percy) and two weeks ago I went off at jct 38 through Percy towards St Lo. At St Lo take the road towards the left towards Cherbourg. (the one by the huge Civil Service building) and then the other side take the dual carriageway at Carentan. However looking at earlier posts the link between St Lo and Carentan may now be in place.

On your arrival at Cherbourg simply look for the overhead signs and there is also a new link road in place for the port.

I much prefer Cherbourg but when we travelled there were limited sailings and we were on the early morning sailing to Poole and thus stayed in Cherbourg overnight.