Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The UIC classification of locomotive axle arrangements describes the wheel arrangement of locomotives, multiple units and trams. It is set out in the International Union of Railways (UIC) "Leaflet 650 - Standard designation of axle arrangement on locomotives and multiple-unit sets". It is used in much of the world. The United Kingdom used a related scheme. The United States uses the simplified AAR wheel arrangement for modern locomotives. It is a more versatile system than Whyte notation, making fewer assumptions about locomotive layout. In the latter notation, some locomotives are impossible to classify, but UIC classification handles them easily. The UIC classification is also much more suited to diesel and electric locomotives.