im not a therapist but these really helped me
i also suffer from an anxiety disorder that is triggered by riding in cars as well, what has helped me the most are practicing calming exercises, yoga, meditation but particularly breathing exercises, i can not suggest hypnotherapy enough and how it should be covered by insurance but its usually not recognized
essentially i discovered i have a deviated septum which already makes it difficult to breathe but i just kinda adapted and didnt know but whenever negative thoughts or if i saw a cop car or somebody swerves in my lane, or just something on the road to spike my heart rate i would have a lot of difficulty breathing through that and end up hyperventilating, and spiraling. even when not driving the idea of being trapped or stranded gives me a feeling of claustrophobia.
so having the tools necessary is incredibly valuable and any good therapist should be able to walk you through those same options to practice before getting in those high stress enviroments, weather it be taking some soothing tea and going to your happy place or also addressing the root cause weather neurological or psychological, theres definitely treatments available thatll hopefully best suit you, good luck ;)