There is one on a road I travel fairly frequently where there is (funnily enough) an obstruction to the view from the minor road joining the major road that can't be addressed without knocking shizzle down. Which is precisely why is has a sizeable (I'd guess 80cm by 60cm) slightly convex mirror, with a big "hey look at me!" chevron border, fitted to the other side of the junction. With this, you can see things what are approaching without edging your vehicle out into the traffic whilst climbing over the top of your steering wheel to squint sideways.
The % of vehicles however that still edge out into the traffic whilst climbing over the top of their steering wheel to squint sideways is rondinculous.
