Nearly all modern monorails work using electric motors that are fed by dual third rails, contact wires or electrified channels attached to or enclosed in their guidance beams. However, diesel-powered monorail systems also exist. The most used monorail in use today is the straddle-beam monorail, in which the train straddles a reinforced concrete beam in the range of two to three feet (0.6-0.9 m) wide. A rubber-tired carriage comes into contact with the beam on the top and both sides for traction and to stabilize the vehicle. The straddle-beam style was made famous by German company ALWEG.