A car can quickly become an oven. Also, animals left alone are vulnerable to theft. For dogs prone to carsickness, consult your veterinarian for remedies. Cats can turn into escape artists on the road, so confine them to sturdy, well-ventilated carriers big enough for them to stand up and turn around in comfortably. Line the carrier with a towel and a tiny litter tray, and secure the carrier to the seat with a belt.
Dogs can travel in a kennel or ride unrestrained.
Stay alert to prevent possible escapes. For added safety, some stores and catalogs sell companion animal restraint devices similar to seatbelts. If your cat or dog is unrestrained, never open a car window or door.