the delta tiller goes some way to alleviate these constraints. The arm-rest mounted controller typical of powerchair designs may be more suitable for many users. Scooters also have fewer options for body support, such as head or leg rests. They are rarely designed for ease of patient transfer from seat to bed. Other drawbacks include longer length, which limits their turning radius and ability to use some lifts or wheelchair-designed access technologies such as kneeling bus lifts. The longer length may also make it difficult to reach door-opener buttons or doorknobs. Some mobility scooter have low ground clearance which can make it difficult to navigate certain obstacles, such as travelling in cities without proper curb cuts (aka dropped kerbs). Navigating in restricted spaces, whether in the home or in public spaces and buildings, can also be a problem. While new public buildings are usually designed with accessibility features, at least in North America, the longer length and wider turning radius may make it difficult to use them. This is a greater problem in older buildings which may have had to make compromises in retrofitting accessibility aids. For example, an elevator or lift may be adequate for a wheelchair, but too short for a mobility scooter. Hallways may be too narrow to make a right-angle turn. Or the "privacy" wall in most washrooms may restrict the entry so that the scooter cannot maneuver around it. However mobility scooters do not have the patient transfer capability to be used inside washrooms anyway. The weight minimum and limitations may be cause for concern as well with the minimum weight requirement being and the maximum being between depending on the make. These limitations may prevent some disabled individuals from using scooters. In addition, scooter limitations may vary depending on model and manufacturer. A limitation of one make/model does not necessarily carry over to all. Individual needs may affect the suitability of a particular model. In general, four-wheel scooters have a larger turning radius than three-wheel scooters. In particular, a purchaser should compare length, width, turning radius and ground clearance to ensure the scooter will fit with most commonly encountered obstacles in the user's environment. Currently in the United States, Medicare will not approve a power wheelchair for persons who do not need to use the chair "inside their own home", even if their medical needs restrict the use of a mobility scooter. For example,