Probably only about 4 hours max from Southern Mississippi to Alabama. I've ran around NYC for a few days alone while a friend worked....but I flew to get there.
Longest was when I moved back to CA from DFW...I did have my mini daschund with me but he almost got left on the highway (he was super needy the entire way). 22 hrs or so.
Craziest was my second year of grad school. My family was all meeting up at my brother's house in AZ. I had to work the night before Thanksgiving and was planning to just enjoy a relaxing, long weekend and miss out on seeing family (even though I could have flown home, etc). Well, while at work that day I decided to surprise my family and left around 7 pm to drive to AZ. I ended up staying in Midland at a Motel 6 for 2 hrs until my dad woke me up (my brother was adamant about telling him in case I needed help throughout the night, something happened, etc)...I forgot to tell him I stopped so we (dog and myself) were on the road again after a very short rest).
14 hours - South FL (FL is the worst!) to the TN/KY border to visit a friend at the military base. Driving around mountains in the dark is crazy. I was 20, and had just moved out of my mon's so I suddenly had this new found freedom. Honestly it was such a freeing trip for me, although crazy looking back.
I used to regularly drive 8 hours from college to my parents house. I didn't want to prolong it either so I would drive straight through with no bathroom or food stops. Just thinking about it now makes my hips stiffen up.
I haven't traveled much since I started driving. When H and I started dating he lived an hour and a half away. That was probably about the farthest trip I've made by myself.
Six hours, from my hometown to our current city, to visit H while we were dating. I wouldn't object to doing more road trips alone, I just haven't ever had the opportunity. We do a lot of trips, though, because my family all lives far away.