I have to say that in my entire life 40++ years now. I have been lucky never to have seen anything like that. I clearly lead a charmed life and am glad of it. The nearest I got was an accident down the street. I didn't rush to look. One I did see was almost funny but it could so easily have been tragic. Back in Dublin city, near Trinity college. A pedestrian crossing, the lights were changing to favour the traffic. I stopped, a girl didn't and dashed across. Meanwhile a biker was filtering through the cars, got the green and accelerated hard. The met in the middle. She tripped over his front wheel, somehow stayed on her feet and ended up on the pavement, with torn tights and a scratched leg, looking shocked. The bike went down and slid quite a bit. The biker was furious, leapt to his feet and berated the poor girl for the damage to his precious bike. Frankly I had little sympathy, even as a biker myself at the time. What he did was stupid. In a busy street, pedestrians always take chances. She was stupid too of course. But it could have been so much worse for both of them.
I don't know if they learned their lessons. But I certainly did.
But I had been trained by my Father, who suddenly took it into his head that I might be a bit careless crossing the road. So he demonstrated. Waited for a car to come and dramatically leapt into the road in front of it. Luckily the driver was paying attention and turned out to be a neighbour, rather bemused looking until my Father explained.
The lesson stuck though.