Yeah... I was at my Dad's in SC for a month and that 1.5 mile bike path was realistically the only option to run a long workout. It made the workout very interesting to say the least. If I had to turn around during the last 5 minutes I would've just ran into the street!
I used to do the latter, especially post college. I just flew the last couple miles during longer runs. The 30 is definitely a bit more on the extreme side but I find that I'm more riding the line than anything. Really the hardest part of it all was the last 7 minutes and the course was mainly the issue. I think flat would've made it much easier.
I tend to be fairly conservative during my workouts but every so often it's nice to take the limiter off and see how the body responds when tired. I don't taper the week for the workout either like I do for my peak workout. It's just another workout in the toolkit.