Curved stair lifts are made to follow the shape of an individual staircase (curved stairs). On staircases with intermediate flat landings they eliminate the need for multiple straight stair lifts by providing a continuous ride up the entire length of the staircase. Because the rail is custom-made to follow the staircase, and because the chair is more complex than on a straight-rail stair lift (it has to be able to remain level while traveling along a track which changes direction and angle), curved-rail stair lifts are more costly than stair lifts for straight stairs.