I would suggest that all speed limit signs should be placed 20m from major junctions and on straight portions of carraigeway wherever possible.
Why does this idea matter?
There are many well meaning motorists who miss a speed limit sign because it has been placed right at the exit of a junction.
Negotiatiing a junction is one of the most hazardous times when driving and a good motorist will concentrate there attention on the traffic conditions, traffic movement, pedestrians and essential singage. Also the angle of view needed when turning through a junction is very wide (and also includes rear and wing mirror checks) so a large area is being scanned. So why place a speed limit sign in the midst of all this when it could so easily be placed just a few metres down the road? In such a location the intensity of concentration has lessened and the sign would be far easier to spot and the line of sight is generally straight ahead.