I don't think you have demonstrated an issue there. Why not slide speeds? Roller-coaster speeds maybe be considered and anyway roller-coaster design engineering expertise to contour the rail so as to manage centrifugal forces when navigating the corners of buildings would be employed. Yes. No. I don't think that's required. I was thinking of something much simpler - simple linear friction to dissipate excess gravitational potential energy on the way down, though the friction would be between the harness hook and the rail, rather than between the mat you sit on and the slide in the case of the helter-skelter. Yes we are agreed on that. To what maximum length of descent are such devices commonly available? I suggest that sky-scraper height lines are too expensive but do please link to the webpage of a commercially available product with prices which proves your point. Well a more parallel system has its advantages of course but I suppose there could be issues with your suggested system like getting tangled up in the lines of other users on the way down. Also if we are talking melting, I would have thought that kevlar lines would be more likely to melt than a steel rail or hook. For durability the rail and hook friction surfaces could be coated with high wear materials such as tungsten carbide. There is certainly a design job to be done to merge the pit stop exit rails with the main rail and ensure hooks merge without jamming. Well you can pay for the maintenance and testing by selling tickets to extreme sports types to take rides down the system for fun. Please Register or Log in to view the hidden image!