The Hog's Back stretch of the A31 is now a dual carriageway, but the two directions of the road are separated by a central area of trees, some of them very old. The original road ran along the stretch now occupied by the lanes running from Guildford to Farnham, i.e. from east to west. The other two lanes, running from west to east, which are a little below the high point occupied by the original carriageways, were added in the early 1970s.