Instead of installing speed bumps have you thought about installing cattle "rails". I am sure the people out in cattle country can give you a better description but here is mine:

There is a trench that is dug into the road and then a piece of square metal with a number of pipes inside is laid into the trench. It looks kind of like a tic-tac-toe board without the vertical lines. They are designed so that cattle can not get out of the pasture area on the road. Having driven over them in the past, you definitely do not want to be going very fast!!!

I am very sorry to hear about your kitty. One of my strays was killed last winter because of anti-freeze so I understand your feelings. Even though they are not inside your home they are inside your heart