Well, that wasn't the actual intent of a Sante Fe (New Mexico) ordinance being proposed, just that dogs should be restrained if riding in the back of a pick-up truck. But it was enough to generate complaints from citizens and now the rule is scrapped. From ABC13.com in Texas:
The city is rethinking a proposed rewrite of its animal control ordinance that would have required dogs to wear seat belts in cars.The city's public safety committee voted Monday to strike a section of the proposal that said any animal confined in or on a vehicle shall be restrained to prevent it from reaching outside the vehicle.
Santa Fe city councilors said they were flooded by complaints about the proposed "doggie seat belts" from residents as well as people in other cities...
...Michael Trujillo, vice chairman of the committee, said the section was deleted not only to eliminate the possibility of seat belts on dogs, but because some people want their dogs to be able to hang their heads out of car windows.