But the acceleration that you are concerned about here is the acceleration (or deceleration) of a car from it's current speed to the speed after the crash. That's the acceleration that has an impact on humans.

A more accurate equation to look at would be kinetic energy = 1/2mv^2. More energy a car has in hitting something the worse the outcome will be.

Now you can say that cars with greater acceleration may be more likely to be driving faster, but it's not a direct correlation of acceleration of a car to the force of impact of the car.