Green cabs

Learner taxi drivers in the UK trundle around on mopeds for years, earning nothing, before qualifying as black cab drivers. Why not have green cabs, however, for learner cabbies. There would have to be some basic vetting procedure before becoming a green cab driver, but this would be minimal [surliness and the ability to fib about having picked up famous people would, I suppose, still be obligatory]. Anyway, if you know the way to where you want to be, you jump in a green cab, direct the driver, and pay perhaps 50 per cent of what the fee would have been in a black cab. This way the driver learns and you, of course, get a good deal. Alternatively, if the driver is learning a new route to, say, Bogton Wharf, that destination would be shown on a large LED screen on top of the taxi. If that happens to be where a pedestrian wants to go, they hail the cab and hop in. Again, if the passenger knows the route and can help the driver by perhaps also pointing things out along the way like "that's St Onan's Hospital on the left" etc s/he likewise gets a discount. Apologies, of course, if such a scheme already exists...