I grew up in the midwest where snow is very much a fact of life as well as horrible drivers. You are also experiencing a pretty bad winter this year too.
I have been driving an hour each way to work for years now. Here shortly - I will be traveling nearly 2 hours to school and another 2 hours home each day. My mind has plenty of time to think about this very issue. We have a lot of deer and other critters that like to dart out into the road, and they build our roads so stupidly that water sits in them and you hydroplane every time it sprinkles. Not snow - but still the same end result of fear.
I am so very sorry that you are dealing with this, and I'm also sorry that you failed your first test. It may not be easy - but you CAN do this. I agree that you need to begin counseling asap. Is there an option to do this through school? I would speak with the school anyway because there are so many aspects of this that they can help with. Maybe they can set up a plan for you so that if you are late, it won't count against you. Not that you aren't coming or won't come - but that late will be ok. Because you may have to make extra stops or go extra slow, it would be helpful to have this available to you. For my program, if we are late - we are locked out. If we are locked out or don't come - its $250 per clinical.
You should also come up with a bad weather plan..... Do you know anyone at school you can stay with when its particularly bad? Keep a few days worth of clothes in your car so that you can stay if it gets bad. Depending on your school, do they have dorm rooms you can potentially stay in? Find some way to have plans to stay in town when its particularly bad.
Most likely you are close to finals for this semester. Do you need to take the Spring semester off? Is that a possibility? If so how would it affect the rest of your schooling? Can you attend during the summer so you are still finished at the same time or do you only have Spring/Fall semesters?
I don't really have answers, but I myself am trying to arrange a place to stay for either a late night / early morning, hurricane conditions, or any other reason that pops up where coming home/going back will be a rough situation. My last resort is a hotel and I'm setting aside about 5 nights worth of hotel money "just in case".
PTSD is very real but you can manage it. I won't even pretend that its easy - but you've made it through half of nursing school - you CAN do this. I was in a situation and 2 years after I was out of the situation it reared its ugly head about 10 feet in front of me. I held my composure long enough to immediately walk away and then for about 5 minutes I was a complete mess. It took another 5 minutes to pull myself somewhat together. I was at work and didn't have the ability to fall apart. I had to get it together and I did. Its been another 6 months and I'm fairly certain I could maintain composure at this point - but its 3 years later. Do not expect yourself to not be afraid - that isn't realistic and isn't good self care. Be understanding of yourself and your fears. You were in a terrible and traumatic situation - allow yourself to be ok with these fears because they are normal and rational. You can also take control and know that you are afraid, but you have to do this for your future. That may mean - taking extra time, going a different route, carpooling or maybe finding a different and temporary housing solution. The bottom line is that its ok to be fearful - just don't let fear stop you. Oh - and a really good doctor is super helpful too!!! You've got this!