We had several in the airport I worked at last. They were a quick and efficient means of making long runs across hot runways in the summer....just leave them by the hangar doors, step on one and zip away.
Segway discovered some problems with their software in 2007-2008 and recalled ALL of the ยฑ30,000 units they had sold/delivered world-wide to that point. Seems a nasty coding glitch could throw the vehicle into reverse without warning and pitch its pilot. Anyway, many of the world's Segways had been shipped to their owners rather than sold through retailers and the recall meant that they would need to be serviced the same way. Many of them were not, and now sit in garages and basements, too dangerous to use or sell. Segway, Inc. claims about 50K units in service world-wide but that number includes those that were recalled but never repaired.
Segways are classified as "vehicles" by virtually every municipality in the country; some classify them as "motor vehicles" while others as "motorized vehicles". There is a difference and that difference determines where, when, how they can be ridden/driven on public streets, sidewalks or other areas. They are still popular as off-road transportation in warehouses, manufacturing facilities, airports etc. but they seem to have lost their appeal as intra-city transportation for any number of reasons.
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Don't confuse enthusiasm with capability...