They just bounce.

My one dog freaked once & jumped out of a tricycle. The other jumped out of my pick-up. Both were tied in & got dragged until it was safe to address the situation. Dogs bodies are made of rubber & their noggins are made of rocks. But it only takes once & they'll learn pretty quick.

I probably seem pretty terrible, but life happens & they were wearing harnesses, leashed & buckled in. So it's not like I didn't do my due dilligence.

Don't be scared. Have fun. Riding with your dogs is a blast for them...and you.