Bathel
Super Boxer
Cerbs just chills in the front seat or will jump into the back seat and lay down on the longer rides. I've never used a restraint for any dog I've owned, and until reading this I never would have imagined so many people do. She'll stick her head out the window unless we're going above 45. I also had to teach her that when I say "shift" she'll brace or otherwise she goes flying when I hit the clutch.
The harness is incase of an accident. If you hit someone or rearend someone at any speed your pup goes flying. A harness can cut the risk of serious injury just like you wearng a seatbelt. I wouldn't dream of driving my pup around in the car without a harness on for that one reason alone. On top of that... I've had a friend with a French Bulldog pup that jumped out the window while traveling 45 mph... wasn't a happy day.
The harness I use clips into a locked seatbelt (like when you lock it for a baby carrier). She can slid up and down the chest strap to move around a bit in the back seat and even stick her head out the window...