at least California has passed a law.
Thousands of dogs die every year from owners who think its cool to take dog everywhere with them, then hit the brakes.
http://www.suite101.com/article.cfm/...g_breeds/25865
It's a common practice among dog owners - taking our furry friend along when we travel by car is becoming easier, especially since motels and hotels are becoming "little dog friendly." Dogs can be spotted with their head hanging out the car window or perched on their owners lap, taking in the view, barking at passers-by or working the steering wheel. Just as people complain about a driver's lack of concentration because they are on a cell phone, having a dog running loose in the car can be a deadly distraction.
Ever slammed on the brakes while driving and feel the force forward? Imagine turning your pet into a flying projectile through the front windshield. Or perhaps, it has already happened to your dog. Every year hundreds of dogs are injured, maimed or killed in car accidents. Just one vet in Colorado reported in 1998 he treated 91 dogs with car-related injuries - 13 died. Multiply that by hundreds of vets in the US. The numbers are staggering.