Botts' dots

Botts' dots (turtles in Washington and Oregon or buttons in Texas and other southern states) are round non-reflective plastic and ceramic raised pavement markers. In many parts of the US, Botts' dots are used, along with reflective raised pavement markers, to mark lanes on highways and arterial roads. They provide tactile and auditory feedback to drivers when moving across designated travel lanes, and are analogous to rumble strips.

Botts' dots are named after Elbert Dysart Botts, a California Department of Transportation (Caltrans) engineer credited with overseeing the research that led to the development of the markers.

Botts' dots are most commonly white but may be yellow when used to substitute for the yellow lines that divide opposing directions of traffic in North America. Many California Botts Dots are made of ceramic, other dots may be made of plastics such as polyester.

On some roads, lanes are marked only with a mix of Botts' dots and conventional reflective markers, eliminating the need to repaint lane divider lines. This kind of substitution is expressly authorized by Section 3B.14 of the Manual on Uniform Traffic Control Devices. Botts' dots and other raised markers are rarely used in regions with substantial snowfall, because snow plows damage or dislodge them.

Caltrans engineers may have studied the concept of raised pavement markers as early as 1936. However, the department did not commence research in earnest until 1953, when the postwar economic boom resulted in an alarming increase in the number of cars and car accidents in California. Painted lines tended to become invisible during rain.

The initial dots were made of glass and were attached to the road by nails or tacks, as suggested by Botts. The nails were soon abandoned: his team discovered that when the dots popped loose under stress, the nails punctured tires. A "former student of Botts named Herb Rooney developed a tough, fast-setting epoxy that could bond the raised reflectors to virtually any solid surface".

In September 1966, the California State Legislature mandated that Botts' dots be used for lane markings for all state highways in all non-snowfall areas.

Today, there are more than 25 million Botts' dots in use in California, though they have started falling out of favor. In 2017, Caltrans announced that it would stop using Botts' dots as the sole indicator of lane division, due to cost and worker safety, and in order to make roadways more compatible with self-driving cars. Reflective lane markings will be wider and thicker, providing some of the tactile feedback the Botts' dots provided. In California, highway lanes may be marked either solely by Botts' dots, or dots placed over painted lines. Four dots are used for broken lines on freeways, and broken lines on surface streets may use only three dots. Reflective pavement markers are placed at regular intervals between Botts' dots to increase the visibility of lane markings at night.