I see people zipping through NYC on these. Usually on dedicated running/biking paths (E River, West Side Highway), but occasionally on city streets and sidewal

I see people zipping through NYC on these. Usually on dedicated running/biking paths (E River, West Side Highway), but occasionally on city streets and sidewalks, as well. I'm always concerned I'll see them hit an unexpected pothole or raised lip at speed and absolutely bite it into traffic.