Roller coasters

I don't understand the point of roller coasters. They go up to 60 miles per hour and all they do is bring you back where you started. If we have a system that transports passengers at 60 miles per hour, why aren't we using it to commute to work? Why aren't we using roller coasters instead of subways? How would you like to get from Manhattan to Brooklyn or Queens in 10 minutes? We have the technology. We have the money. What is the problem?