> Drivers in the UK must be able to read a number plate from 20 metres away, according to the Driver and Vehicle Licensing Agency (DVLA).

I would like to see better tests. I have a pet theory that visual perception deficiencies along the lines of simultanagnosia are considerably more common among older people than is generally recognized, and people with these conditions may be able to easily read letters and numbers at a distance but be unable to drive safely due to inability to reliably detect obstacles.

Visual screening is fairly easy and every bit as quick, but it needs different tests. Something along the lines of an Ishihara plate but with colors that are perceptible even to color blind people might work. Or a visually busy image with instructions to identify one or two particular objects in the scene.