Raised pavement marker

A raised pavement marker is a safety device used on roads. These devices are usually made with plastic, ceramic, thermoplastic paint, glass or occasionally metal, and come in a variety of shapes and colors. Raised reflective markers, such as plastic, ceramic, or metal ones, include a lens or sheeting that enhances their visibility by retroreflecting automotive headlights, while glass road studs gather automotive headlights with a dome shape and reflect the lights with a reflective layer within. Some other names for specific types of raised pavement markers include convex vibration lines, Botts' dots, delineators, cat's eyes, road studs, or road turtles. Sometimes they are simply referred to as "reflectors".

The surface of this type of vibrating coating line is distributed and scattered with raised bumps. Some bumps are coated with high-refractive-index glass beads. When a speeding vehicle runs over the raised road lines, it produces a strong warning vibration to remind the car driver of deviation from the lane. Perpendicular to driving directions, these marking lines are used for settled mainline toll plaza, ramp entrances, mountainous areas, continuous sharp turns, downhill sections and the end of the highway (intersection of highway exit and the plane of the common roadway), gates and entrances of enterprises, institutions, and school. In the same direction of traffic driving direction, they are mainly settled in the median strip, edge lines, and dangerous sections of the road.

In the United States, Canada, Mexico, some countries of South America, Thailand and Australia, these plastic devices commonly have two angled edges facing drivers and contain one or more corner reflector strips. The marker is generally held in place using butyl pads, epoxy glue, or bitumen. In areas with little snowfall, reflective raised pavement markers are applied directly on top of the road surface. The device's retroreflective surface enables the device to be clearly visible at long distances at night and in rainy weather. The devices come in multiple colors in accord with local traffic marking standards.

In 1965 San Diego Police Motorcycle Officer Kenneth Grant Maine, improved upon and applied for a patent on the white epoxy-resin reflective raised pavement marker. He then submitted it to the California Bureau of Highways, later called the California Department of Transportation, which is now known as Caltrans.

In areas where snowplowing is frequent, conventional markers are placed in a shallow groove cut in the pavement, or specially designed markers are used which include a protective metal casting that is embedded in recesses in the pavement, allowing the marker to protrude slightly above the pavement surface for increased visibility, much like a cat's eye.

Lit LED in-pavement Raised Pavement Markings (RPMs), help improve road safety, as they are more generally visible than reflective RPM markings as they are internally lit and don't require headlights to show up. The RPMs are usually raised for visibility, but in snowplow areas these types of RPMs can be installed flush-mounted within the pavement to avoid the snowplows.

There are a number of types, ranging from a single LED point source RPMs, with limited daytime visibilities, (road studs), to multi-LED linear type RPMs, visible in all full sunlight and nighttime applications.

Some lit RPMs can be visible and useful in both bright sunlight as well as nighttime applications, whilst others are only visible at nighttime or in low light applications.