I started doing out-of-town road trips with my friends when I was 17. We would usually cross the border into the US (Minnesota) and drive to Duluth for the day. I don't see a problem with that but your mother does, and I don't get a vote.

How would she be likely to react if you just left early in the morning and told her you would be gone all day, without providing details? Is she the 'grudgingly accept her little boy is growing up' type or the 'call the police and accuse you of stealing the family car and kick you out of the house' type?