A train that runs on or is suspended from a single rail or beam is called a monorail. Unlike traditional railways that use two parallel steel rails, a monorail vehicle is typically wider than its support guideway and either "straddles" the beam (straddle-beam) or "hangs" from it (suspended). The most famous examples of straddle-beam monorails are found in Disney Parks and Tokyo, where rubber-tired carriages grip the sides of a concrete beam for stability. The Wuppertal Suspension Railway in Germany is the most iconic example of a suspended system, operating since 1901. Monorails are favored in urban environments and airports because their elevated design requires a very small "footprint" on the ground, allowing them to pass over existing traffic and buildings. While they are often associated with futuristic aesthetics, they are highly practical for medium-capacity transit where traditional heavy rail infrastructure would be too disruptive or expensive to install.