True, I think lanes=1.5 would fit better. On the second point, I think you're right; it's narrow and twisty in places and Purton isn't even signed along here from the Common Platt / The Pry turn. 

The only thing is that Purton generally doesn't have many quality roads around it and tertiary differentiates between Collins Lane north of here, which is narrower still. But Manor Hill / Church St is signed for Purton and actually has road markings in places so downgrading this would be logical.
