Clear sign needed to prevent inadvertent entry against one way traffic

The service road that runs from London Road to LocknStore is one way. Only westbound traffic is permitted. However this is very poorly indicated from the west end. Cars legally coming north from the Whitworth Way roundabout may well not see that they are not allowed to turn right onto the service road. I have on three occasions met vehicles driving east against the one-way system. The only signage is the words 'no entry' written on the road. However these words are not readily seen by cars coming from the Whitworth Way roundabout. Moreover if a westbound car is turning towards the roundabout, it may completely cover the no entry words, as seen in one of the accompanying photographs. I think that there should be a very clear no right turn sign for vehicles coming from the roundabout