Travelling with a four legged friend must be a pleasure but safety both for him and for us is fundamental.
On sale there have been objects suitable for this for years.
For the ones who have medium and big sized dogs, I would opt for a separation with grids suitable for any car to be put at the back of the back seats.
If you have not so quiet pets, I would suggest boxes to be put in the back space with the suitable size according to the one of the guest.
You can find them both of metal and of plastic: this second option is to be preferred because more comfortable, easier to clean, lighter and more manageable.
For smaller subjects, normal carriers or comfortable soft structures with safety belts are better.
Only quiet subjects can be free in the car, for long travels use a soft cushions to be put on the back seats.
I never suggest to travel with the dog on the driver’s knees, it could be not only a reason of distraction but the animal could be scared or have sudden reactions that could be very dangerous.
In these days on the web and on social networks you can see the advertising of a container for small sized dogs to be used in the cars
It is a sort of a soft small seat where a system of velcro belts ties the subject who has a completely unnatural position, form the one at four legs he is like “ hung” in the standing one without resting the back paws.
This position, above all if used a lot in time, could provoke heart and circulation damages.
It is correct to contain them for their and our safety but always respecting their structure and letting them have a comfortable position according to their size and their health conditions.
For cats the carrier with the correct size will be the ideal solution.
If cats are two or more, it would be better that each has his own, so that they could lay without bothering each other.