You may have thought of all of these things but I would think some options might be:

Hypnotism. I used it for fear of flying and it worked. It "wore off" after about 12 years though. But truly, I was able to fly without an ounce of anxiety.

EFT. I use this for anxiety and although it looks weird, it really helps and you can use it anywhere. http://eft.mercola.com/

Propranalol is another option. It is a medication that can block adrenalin release and regulates heart rate which can prevent or resolve anxiety. No deleterious affect like tranquilizers either. And you can take it every day or as needed.

Also, of course, moving closer to work, telecommuting, car-pooling, busing in, asking for a change of schedule so you can avoid the bulk of traffic.

Don't know if any of these things would work.

I find that listening to music calms me in traffic.
Or listen to a book on tape. :)

I get driving anxiety and avoid freeways. I take older roads even though they take longer. For me, music helps a lot. Good, upbeat songs with power. What people sometimes call good driving music. I don't know if you're into this, but I also pray before I drive and also when I arrive home safely. I take my meds in the morning, but one f them I can take at *whatever* time during the day, so if I have a long drive ahead I will take it shortly before I leave to drive. I also drive very, very defensively. I stay in the slow lane. If I'm really having a hard time, I pull the car over for a few minutes.

Still, I know all about driving panic attacks, and they are awful. I hope the situation gets better for you.

I have an hour commute everyday and it is already wearing on me. This is a new job, so by the end of the school year I am sure that I will be ready to quit. I don't get anxiety about the commute. But giving my brain two hours a day to just think is not a great idea. lol
I am going to be commuting with another teacher at my school. That may help. Have you thought of something like that? A person talking to you is very distracting.

Ask yourself what it is that stresses you out most. Is it fear of getting in an accident? Are you afraid that you will lose control if another driver makes you mad? Or are you just dreading the uncomfortable feeling of sitting in a car for so long every day?

There is research that suggests long commutes are very unhealthy and take a toll on the body. I would suggest making sure you get a lot of exercise and perhaps try yoga. There are probably even some yoga techniques you can use in the car to help release tension in the muscles and focus on your breathing. I think in the long run, you should think about moving closer to your job or telecommuting if it is at all possible.

I commune 100 km each day every day. From time to time, esp when I am feeling down, I also get commute anxiety. If I am not driving, I call up friends and talk to them on the highway or listen to music and try to read a book. Talking to fellow commuters (as long as they are not creeps) also help. However if I am the one driving, turning up the music and singing along to my fave songs help.