For my 17 yr old cat, I last bought her a small dog harness, with a strap around her head, a straight strap that goes to the bigger, stomach strap, that one goes around her stomach, with her two front feet in it, and hooks with a smaller plastic snap. She could NOT escape from it. She really didn't like it, and when I had it in my hands she would run and hide. I had trained her that when I spoke harshly, sho would come to me, finally.
I would slip her head in the front part, adjust it to be snug, not too tight. Then snap the second strap, and adjust it too. Then before we ever left the house, the leash went on, so if, God forbid, she would be out of the vehicle, I would have an even better advantage to catch her.
It worked very well, and she could be put out on a high-hanging rope, on a pulley wheel, a long strap and she could be outside as long as I was there, with no problems.
She is gone now, so I don't have to worry about traveling with a cat anymore. But, she really did like to travel, she would sit in my lap, as the passenger, and watch out the windows watching cars, trucks all the good stuff go by. Wasn't afraid at all. Would soon be bored and go to the read seat, and go to sleep. Must have come forward to say, " Are we there YET?" lol