In your introduction you say you have -5.0D?!?
That’s not the same as @Ursa driving without glasses!
If that’s the opto’s current prescription for you, you should have full clarity for driving with them as a starting point in my opinion. (Or have you missed the last few checkups and you may as well be -5.50 or -6.00 by an opto’s measurement?)
60ft for a big road sign is a good reference point for clarity…
From your intro and topics / posts I guess you are an enthusiastic beginner. I’d recommend getting a pair of glasses that gives you full clarity for the most challenging vision situation (e.g. night driving) and use them for distance vision, and especially when clear vision is crucial. Or if your current full prescription is fresh from the opto, then just wear it to remind your eyes what distance clarity is.
Otherwise it’s advised to spend a few weeks working out the centimetres for close up - how much it changes (with different lights, within the day, between days). You’ll need good data to work out the best first differentials for you and for your child.
And when you have full clarity at distance and you have reduced differentials successfully, that’s when it’s advised to reduce normalised first, but not to zero diopter…