Higher driving speeds lead to higher collision speeds and thus to severer injury. Higher driving speeds also provide less time to process information and to act on it, and the braking distance is longer.
The higher the collision speed, the more serious the consequences in terms of injury and material damage. This is a law of physics that involves the quantity of kinetic energy that is converted in an instant into e.g. heat and matter distortion. In addition, the human body is physically very vulnerable in comparison with the enormous forces released in a collision.
You seem to be trying to suggest that he was going at walking speed and the dead woman has just tripped over awkwardly. Farcical nonsense as usual.
Speed kills, and that is an accepted fact.