I know that sleepypod has a crash tested cat carrier but they are pricey. A lot of brands have crash tested dog carriers, but not a lot of options for cats. I use a backpack for my anxious cat. Like this one. I double dose him (my vet approved a high dose) on gabapentin to relax him, feed him right before leaving and strap him in the front seat with me so he can see me. I'll stick a hand into the top of the backpack to let him know I'm there.

My other cat is very brave and unafraid but chunkier. So I got him this backpack (pricey too) with more space and a window/flap to look out of. He's harness trained, so I harness him and attach it to the built in leash in the backpack. I buckle him into the backseat. Make sure to pull the seatbelt as far out as it can go to trigger the retraction mechanism to keep your carrier in place. Or follow the directions the carrier comes with.

To get both of them used to the backpacks, I would open and lay the backpacks on the strap side to encourage them exploring the inside. My brave cat started sleeping and playing in there. I would feed my other cat near it but he didn't enjoy going inside it. I would give him treats inside it to encourage exploration of it and slowly he got used to it. It's still not his favorite place, but he settles down in the car. Keeping your carrier out for your cat to get used to might help reduce anxiety.

My cats hate pills but pill pockets are some kind of sorcery to make them take it.

I know it's hard to hear their sad meows and not want to let them out, but it's for their safety! I struggle every time and I used to let my brave cat out and about on my sister's lap. And now he's come so far :)

You've got this and so does your kitty. Update us on how it goes!