[JoeAltmaier]

Right - a head-on collision between objects of equal mass and velocity is equivalent to one hitting a brick wall (or immovable object) - it loses all its kinetic energy on the spot, turning it into heat and mechanical work (e.g. crushing the car and driver). Objects of slightly different mass or velocity means the work done on each is shifted, the heavier or faster one 'winning' a bit but still. The absolute values of the velocities are hugely important.

[tertius]

Agreed regarding absolute value, my usage of differential is not comparing different scenarios but focused on one.

So 25 mph + 40 mph in a 25 mph is dangerous.

80 mph + 55 mph in a 55 mph is dangerous.

Obviously the former has much less energy, but within itself, the differential is what creates the most accidents and danger.