Sadly some cats do not have much road sense and do bolt out right in front of cars. I've seen a cat killed, bystander, no my car nor my cat, and the cat was under a parked car and just ran out. Poor driver was really shaken, poor cat too of course.

Main difference with dogs is if you hit a dog in the street your first thought is "where is the owner?!" and there'd be a reasonable case to be brought against the person that let their dog just wander the streets. While ever cats are considered independant and 'feral' enough to wander around rounds on their own they'll be treated differently. It's sad but if you let an animal walk around on roads by itself you have to expect to lose some to road accidents. It's not always the result of lazy or cat-hating motorists. A small furry bullet can be hard to miss when it zooms in front of you. The law you talk about, what would it say and how would it reduce the number of cats killed on roads?