I've always thought of Preston as a city... sort of a west-coast version of York. But if the whole area was designated a new town, that would explain why the postcodes in Chorley start off with PRThen again so does Southport which is surprising as you would think it would have a Liverpool postcode. In fact the PR postcode boundary covers a wide area including most of the rural parts of the Fylde Coast and the western Ribble Valley area.
What I notice with new towns is the single bracket columns on main roads have sharp corners whereas the type commonly used elsewhere has the rounded version like the one nearest the camera.Very well observed! Well strangely enough I noticed a long time back that the older metal columns around Preston, Chorley and South Ribble have the angle-edged brackets. I always wondered why this was. They're particularly used in the suburban areas of Preston and the main roads that connect Preston with Chorley including the A6 and all around the 70s/80s Walton Summit and Clayton Brook areas. At one time these were the most commonly-found main road columns in Chorley borough (possibly still are) and have a slightly different design to the Preston and South Ribble versions as the bracket looks a bit thinner compared to the column on the Chorley versions.