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Dismo...once he had realised his mistake, there wasn't much alternative. Reversing back up the ramp would have arguably been more dangerous.
Sometimes road layouts are very complicated and mistakes can occur. Very early one morning last December, before it got light, I went around a roundabout the wrong way, outside the entrance to the Exeter Services on the M5. I have driven over that route many times in the past but it was dark and very misty. Luckily there was hardly any traffic, except a friendly lorry driver who waved me down. No harm done but it could have been different a few hours later, when the area was thronged with traffic. My excuse is that that particular road layout is very complicated at the best of times. There loads of signs, all over the place and you can't see the wood for the trees sometimes.
There for the Grace of God, etc, etc.