Under the Welfare of Animals (Transport) Order 1997, you must not transport an animal in a way that causes, or is likely to cause, injury or unnecessary suffering to that animal. It is also important that a dog is suitably restrained in a vehicle so that it doesn’t distract the driver or injure them if the vehicle stops quickly (UK Highway Code). The RSPCA therefore recommends that dogs are both secure and comfortable during transport.
There are a number of different ways in which you can restrain your dog comfortably during transport. Travelling crates and containers are popular. When transporting your dog in a crate or container, you should ensure that it has enough room to sit and stand up at full height, turn around easily and lie down in a natural position. You should also ensure that your dog is able to see out of the container and that there is enough ventilation and airflow. Suitable bedding should be placed on the floor to prevent the dog from slipping around during the journey.
You could also consider a car harness that secures your dog by linking in with the seat belt system. To ensure comfort and security, you should make sure that you measure your dog correctly and buy a harness of the right size. Always follow the instructions and ensure that you fit the harness correctly.
Other useful information:
The dangers of leaving a dog in a car on a warm day