Panting or yawning
Pacing or restlessness
Drooling
Being unusually quiet
Excessive swallowing or lip licking
Vomiting
Diarrhoea
Whining or barking
Withhold food for 3-4 hours before the car ride. An empty stomach may help with the feeling of nausea.
Give them a view. Looking out of the window helps the brain deal with conflicting sensory information that can cause motion sickness.
Stop regularly. Having a break from the car for a walk, a wee, and a sniff can help your dog feel better.
Keep them restrained. This can help if your dog is anxious and paces in the backseat and provides a level of safety during car travel.