I don't consider the humble Segway to be all that safe. The owner of the company drove one off a cliff, after all! But some foolish individuals modified their Segway to go much faster than originally intended.
The mod was pretty straightforward: they added bigger wheels. But that was enough to get it going at up to 25 miles per hour. Doesn't seem like much in a car, but try doing it while standing upright on a two-wheeled death platform. No thank you!