I agree with CRX-YEM if you cannot trust her then what is the point of the relationship. She want to go out and experience the open road. I have done the drive from san francisco to Tucson some thing like 15 hours by my self, it sucked. My point is that you probably would go on the road trip by yourself if you had to, and it is probably not the smartest move relationship wise to create the double standard. If she told you this is what she is doing rather than going behind your back there are good intentions about this and if you are really paranoid about it just ask for her to call you every now and then.