In my state, it is MY decision, whether or not to become involved if I am not at work.
When I touch a victim, I am legally required to perform "to my highest level of training" and you are legally responsible if you do anything that is OUTSIDE of your scope of training/practice.
Before I became an RN and was a student, I did not realize that trauma care required very specialized training to do this out in the field. You will typically not have the equipment if you respond by yourself.
Don't think that you have a secret "super RN" cape flapping behind you. People go 190% of the deep end (with no legal case to back it up) that you have anything nurse related ie. bumper stickers on your car and drive by an accident and do not stop that you can be sued....that is about as big of a myth as the Easter Bunny.
You could have a child in the car, you could be on your way to another emergency, or even better, it may not even be YOU driving the car.
Now, some states do require that if you are the first to come upon an accident that APPEARS to have injury, you are required to GET assistance, not necessarily RENDER assistance...but I don't live in one of those states.
Use your head....did you learn anything in school regarding your LEGAL REQUIREMENT to respond outside fo the facility?
Of course you didn't....there is a reason for that.