A transit system consisting of vehicles supported and guided by a single guideway (rail or beam), usually elevated. The basic types are as follows: supported, in which vehicles straddle the guideway or are laterally supported by it; and suspended, in which vehicles hang directly below the guideway (symmetrical monorail) or to one side of it (asymmetrical monorail). Supported monorails are stabilized by gyro, overhead rails, or lateral guidewheels on both sides of the beam (saddle monorail). (TRB)