Molly was dreadful in the car at first - it sounded as if I was murdering her. I took her out in the car three times a day, but no longer than 2 minutes drive each time (ignoring the howls) and made sure she had a lovely time running around off-lead at the end of it. Within a short time she was happy in the car. I gradually took her on longer journeys and by the time we’d been doing it for a few weeks we went on a four hour journey (with breaks) to visit relatives. This was possible for me because I live within a couple of minutes of a recreation ground and the beach - I know if you’re in the middle of a city it might be trickier to use that method.
Start by just popping puppy in the car and click and treat for remaing calm. Repeat for several days. Next step place puppy in car and sit in driving seat click and treat puppy for calm behaviour. Then start car reward puppy for remaining calm. Then drive to end of road, turn around and drive home reward puppy for remaining calm. Gradually extend the distance and reward puppy for remaining calm. Slow progression helps puppy to build confidence in being in the car. Also pop puppy in the car fir trips to the oark fir nice walks, not just trips to the vet, to help build positive connections to the car.
nice & slow, start with not even going anywhere, rewards for sitting in the car, calmly - super advice from @Jojo83
I did exactly what @Jojo83 advises earlier this year with my puppy. It really paid off. We can go anywhere.
Short journeys to nice places worked a treat for us. Before long all of our dogs enjoyed the car and associated it with nice things.
Cooper was very nervous originally, but with short fun rides, to fun places she go over it in a week or so, and now she loves to ride. Her first big ride was with the breeder, bringing her all the way across Oregon, away from mom and siblings, and then she met her strange new family. No wonder she was a little nervous at first. I don't recall Tilly ever being nervous about rides, though she did get car sick a couple of times.