Botts' dots (low rounded white or yellow dots), named for the California Caltrans engineer Elbert Botts, who invented the epoxy that keeps them glued down, are one type of a mechanical non-reflective raised marker. Generally they are used to mark the edges of traffic lanes, frequently in conjunction with raised reflective markers.[citation needed] Botts' dots are also used across a travel lane to draw the drivers attention to the road. They are frequently used in this way to alert drivers to toll booths, school zones or other significant reduction of speed limit.