"Unlike cars, motorcycles and bicycles, Segway doesn't fit comfortably in any traditional transportation categories. By the letter of the law in most states, Segway should be regulated as a motor vehicle, which would restrict its use to the street. The company fears this classification would be a death warrant for Segway, if not for more than a few of its users, hence the intensive lobbying and public relations efforts by company officials. The tab so far: $741,000... The main opposition to allowing Segway on sidewalks comes from pedestrian advocates who think sidewalks are crowded enough already. They don't want Segways buzzing past or running into them as they stroll down the street."
Thanks to Chris Steins