Road Surface Marking and Markers

Mechanical Road Surface Markers

Mechanical road surface markers are generally raised or recessed into the road surface and may be reflective. Most mechanical markers are permanently installed, although they can be moved or modified based on needs and capabilities. The main types of mechanical road surface markers in the United States are “Botts' dots” and rumble strips.

Botts' dots are named for the California engineer Elbert Botts, who invented the epoxy that keeps the raised white half-spheres secured to the road surface. Botts' dots are low to the ground and are nonreflective. They are used most frequently to delineate the edges of traffic lanes and are sometimes used across travel lanes to keep drivers' attention on the road. In addition, this type of road surface marker is used to make drivers aware of school zones, upcoming toll booths, and significant speed limit restrictions.

Because Botts' dots are raised off the road surface, they are not as suitable for road surface marking in regions where snow plows are used regularly [Page 1179]to scrape roadways for snow removal. Another marking device known as a “cat's eye” takes snow plowing into account. It is made up of four reflective lenses mounted in a durable white rubber housing that is mounted into a cast-iron form. The rubber housing sinks into the form when a vehicle moves over it, providing a relatively smooth surface for plows to pass over. A self-cleaning mechanism wipes the lenses each time the device is depressed. This type of marker is used widely, but mainly in Great Britain and Ireland.

“Rumble strip” refers to a series of shallow channels that are ground out of the pavement on a roadway to create a vibration and intonation when a vehicle passes over it. The vibration and sound are intended to alert the driver about approaching hazards or areas that require reduced speed and caution. Raised strips that are adhered to the road surface serve a similar purpose, creating a vibration and sound when a vehicle passes over them to warn the driver.

Road surface markers that have reflective surfaces are commonly used as lane dividers and to indicate exit and on-ramp access roads. The incorporation of a raised retroreflective element into the marker makes it more easily visible in the dark and in inclement weather circumstances, such as driving rain or snow.

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