Side friction roller coaster

A side friction roller coaster is an early roller coaster design that has two sets of wheels – normal road wheels and side-friction wheels to prevent the cars from derailing on sharp curves. In comparison, modern roller coasters have a third set of wheels, called up-stop wheels, that allow them to perform steep drops, whereas side-friction coasters almost never featured drops of steeper than 45 degrees.
An even earlier design, the scenic railway, used only road wheels, and was thus incapable of sharp turns and steep drops, and usually required a brakeman to ride on the train and slow it down when necessary. Their name derives from the fact that they are often adorned with elaborate façades.
History.
The side-friction coaster was invented near the beginning of the 20th century. The most common design was, by far, the stacked figure-eight layout, with dozens appearing in parks throughout the world. This version often went by names such as "Toboggan Slide", "Drop/Dip/Leap the Dips", or simply "Figure Eight", and featured tiny drops.
Other side friction coasters, such as the giant coaster at Crystal Beach Park, were built in a style similar to modern wooden roller coasters, and featured large drops and extremely rapid turns.
The invention of up-stop wheels in the 1910s allowed much more scope for height, speed, and steepness in coaster designs, leaving side friction coasters to quickly fall out of favor. Only a handful have been built since World War II, and none since 1961. Today, there are only two side-friction coasters left in the world, and nine scenic railways standing, with 8 still operating. One of the most recently closed examples was the "Runaway Coaster" at the defunct Rotunda Amusement Park in Kent, England, which was closed in 2003 and demolished on April 5, 2007.