Sorry for the delay it took longer than I thought. It sounds like an attention getting behavior but I also want to cover other reasons for dogs to "act up" on car rides. Often motion sickness iwill cause behavior issue. It may not be causing him to vomit, but may be making him uncomfortable. Motion sickness is worse if you can't see out a window. Some people use Benadryl to calm their dog before car travel and Dramamine is also used for motion sickness, but your Vet should be consulted before using Dramamine.
Benadryl can be given to your dog, the dose is up to 2mg per pound every 8 hours. The dosage for Dramamine (Dimenhydrinate) for motion sickness is 2-4 mg/pound by mouth every 8 hours.
Any medication should be given an hour in advance to car trip.I have a dog that used to constantly pace and jump around the car as well and no training would help, but Dramamine helped even though he wasn't actually vomiting.
For anxiety, herbal rescue remedy is often used, but another option is a DAP collar that uses pheromones to calm a dog. It emits pheromones similar to those produced by a mother when nursing pups. You might try giving the medication, waiting an hour and then put him in the car and just move up the driveway slowly so he sees that it isn't the same as it is normally. He may still be anxious since he is used to it making him uncomfortable, so I would still use a DAP collar so he is calmer as well.
Now if it is stictly behavioral you will have to train him not to bark. It will be best if you have someone else drive while training for no barking in the car. While you are going down the road, when he barks, you need to give him a correction. A correction is a short tug on the leash and a firm low toned "NO". You need to be consistent and give a correction each time he barks. As soon as he stops barking, even for just a minute or two, reward him with calm even praise and a hot dog slice (treat). These treats work better than normal treats as the dog sees them as high value. As he learns that not barking gets him treats, require he be quiet longer. You can and should also use the command "no bark"or similar command so you can use it at other times. Once he is quiet when riding, you take over the driving and see it he doesn't stop barking on command. Still feed treats as rewards.
I'd also start working on the quiet command. As crazy as this sounds you may wish to teach the pup the speak command and then the quiet command. It seems easier to teach the quiet command after the dog has learned the speak command. The following site explains teaching speak and quiet commands.
You also have the option of getting a bark collar such as citronella spray collar,or a shock bark collars that stops excessive barking. They are effective and both work.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time.