From the ground we look up the side of an imposing city skyscraper. A man is climbing precarious scaffolding to its giddying heights and, as he reaches the roof, we discover it is sixteen storeys high. He steps serenely to the edge and dives from it. While he rapidly plummets, we are told that an unbelted passenger in a 1ookm/h collision would sustain the same impact as his fall. Thankfully, like a Mercedes passenger, he