I a big fan of singing in the car too. When John Lennon was in his Primal therapy phase he made some recordings that are simple blues patterns and basically exercises in vocal variety. I'm thinking of well, well,well or why do.t we do It in the road. Not musical masterpieces. But sing them in the car or shower and let your voice go, to whatwver you are feeling. Its expressive and It does something to the central nervous system as well. Again, you have to be aware of prevent reality no abreacting, stay present and Drive. I've been intrigued by how much easier It is to connect emotionally to people irl when I have been singing. I suppose its just bringing emotion to the voice, instead of buried deep inside. I've been surprised by the emotion in my voice sometimes. I wonder if It would work as well for a trained singer.