1) A geometric scaling of the number plate test to a Snellen Acuity gives an equivalent of 6/15 but this does not usefully predict the result of a number plate test as the fonts, contrast and test conditions are very different.
2) Drasdo & Haggerty found that a binocular visual acuity of 6/9-2 or 6/10 gave a similar pass rate to the number plate test but did not necessarily fail the same individuals.
3) The EU Directive requires a minimum binocular Snellen visual acuity of 6/12 in a clinical setting. This is not currently the UK standard. It should be!