We have a very nervous border collie as well. She was pretty sensitive to a lot of things especially when she was young. But exposure and her getting older helped with it. You could probably just google turn signal sound effect and there’ll be ones not on YouTube.

Our border collies are pretty good in the car but we also use a very secure harness so they don’t get to walk around in the back seat. Seems to help keep them relaxed as well because they fall asleep all the time. Also recommend crate training especially if your dog tends to damage things when bored.