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A monorail serving as a track for passenger or freight vehicles.In most cases rail is elevated，but monorails can also run at grade，below grade or in subway tunnels.Vehicles are either suspended from or straddle a narrow guideway.Monorail vehicles are wider than the guideway that supports them.

There are two major types of monorail systems.In suspended monorails，the train is located under the track，suspended from above.In the more popular straddle-beam monorail，the train straddles the rail，covering it on the sides.There is also a form of suspended monorail developed that places the wheels inside the rail.

Supported or“straddle”monorails，with a single rail below the train，include the Tokyo Monorail；the Schwebebahn in Wuppertal is a suspended monorail，where the train body hangs below the wheels and rail.Monorails have never gained wide acceptance except for Japan，although Seattle has a short one，which it hopes to replace with a new，larger system，and one has lately been built in Las Vegas.One of the first monorail systems in the United States was installed at Anaheim's Disneyland in 1959 and connects the amusement park to a nearby hotel.

Modern monorails are powered by electric motors and usually have tyres，rather than metal wheels which are found on subway，streetcar（tram），and light rail trains.These wheels roll along the top and sides of the rail to propel and stabilize the train.Most modern monorail systems use switches to move cars between multiple lines or permit two-way travel.Some early monorail systems noticeably the suspended monorail of Wuppertal（Germany），dating from 1901 and still in operation have a design that makes it difficult to switch from one line to another.

Monorail systems have been built in many countries around the world，many of them on elevated tracks through crowded areas that would in another way require the construction of expensive underground lines or have the disadvantages of surface lines.