Speed shapes

On an unfamiliar road, approaching a speed limit sign. It's a red circle with black figures in it, so it's not a 'national speed limit' sign (UK). Does it say 50? 30? 40? 20? I'm still too far away to tell.

Or maybe it's just time I had my eyes tested.

I can brake early, in anticipation of a 30mph zone; lose momentum; reach what then turns out to be a 50mph zone and have to re-accelerate, wasting petrol.

Or, I can assume it's a "50" sign; realise too late that the sign in fact says "20", and have to brake late & hard. Oooh, dangerous. And bad for your brakes.

Now, if speed limit signs were different shapes, they could be read at more of a distance ... driver anticipates required accel-/deceleration earlier, safer braking, more economical use of fuel, traffic moves more smoothly.

Bosh.

I propose the 30pmh sign remains a circle. A stretched ellipse (with the long axis on the vertical) for 40pmh, some kind of rhomboid for 50, and a 5-pointed star for 20mph zones past schools and residential areas.

Of course, it won't help the swine who choose to do 80 past my house (40mph limit). They'll get theirs. I've seen the road-death figures for this county.

A measure of international standardisation in sign-shape would be welcome, and perhaps some commonality between signs in mph and their approximate equivalents in km/h.

We've been here before, I know, and people have objected about the expense of having to mass-change thousands of road signs. Well .... yeah.