We've been doing these since 2005? or 2006? with very few issues (and very few incidents for that matter) and NASA's blessing. We use the HPDE tech sheet because that's how it is technically sanctioned & insured due to the higher speeds. But it is still a solo event with 2 or maybe 3 cars on track at a time at ~30sec intervals, just like an autocross on a course with no crossover. It doesn't have a separate set of rules because, so far, it hasn't needed 'em. Although there are a few roadcourse-event-specific things we talk about in the Circuitschool and at the main drivers meeting that are definitely things you won't hear at a regular autocross (or autox school.)

Short version is, come see for yourself... it's a whole lot of fun