Whilst on a business trip in Holland, I noticed that at least some of the major roads there seem to have a screen dividing the carriageways (as well as ones at the edges to reduce the escaping noise in urban areas, I imagine). This seems naively like a rather good idea - there's almost no circumstance in which I can imagine that being able to gawp at the other carriageway is actually helpful or liable to increase your safety. Well, unless perhaps a lorry is about to plough through the central reservation, but the odds of your being able to do something useful in that situation seem rather low in any case...