Pavement marker (roads)
A Pavement marker is any kind of device or substance that is used on pavement to convey information.
In general, these devices are either mechanical, paint or plastic. They can be used to mark the edges of traffic lanes, or serve as noise generators when run across a road, or attempt to wake a sleeping driver when installed in the shoulders of a road.
Mechanical devices can be either raised or recessed into the pavement and either reflective or non-reflective. While generally permanent, they may also be moveable.
Bot dots (low rounded white dots), sometimes called Botts' dots after the California engineer who came up with the idea, is one type of a mechanical non-reflective raised marker. Generally used to mark the edges of traffic lanes, frequently in conjunction with raised reflective markers.
Bot dots are also used across a travel lane to draw the drivers attention to the road. They are frequently used in this way before toll booths to get the drivers attention so they slow down or when a significant drop in speed has happened like going into a school zone. They are normally only used in warm climates since snow plows usually remove them along with the snow.
Reflective markers, known as Cat's eye in some countries, are normally used as travel lane dividers. By being reflective, they are more visible at night and in inclement weather. White is generally used to indicate a travel lane in your direction of travel. Red is used to indicate a travel lane opposite to your direction of travel. Yellow is used to indicate that traffic on the other side of the line is moving in the opposite direction.
These markers can also be used for other purposes such as marking the locations of fire hydrants (blue) or at gates to gated communities to indicate that emergency service vehicles have a code or device that allows them to open the gate. In some countries like the UK raised markers are also used to mark crosswalks to assist the blind in crossing streets.
In colder climates, reflective markers can be installed below ground using an elongated narrow triangle, cut into the pavement that allows the device to be installed below the road surface.
Rumble strips are sometimes installed on the shoulders of a road to wake up a sleeping driver who has drifted out of a travel lane onto the road's shoulder. Tires running across the trenches cut into the surface make a lot of noise and shake the steering wheel.
Pylons are sometimes used to separate HOV lanes from regular traffic lanes. They are also used in areas where lanes are used at different times for travel in both directions. These pylons have shafts that drop into holes in the pavement. A good example of this type of use is the Golden Gate Bridge in San Francisco.
Plastic is commonly used to mark crosswalks, stop lines and traffic guidance such as turn lanes, HOV lanes, train crossings, pedestrian crossings, taxi lanes, and bus lanes. The plastic is applied by heating and then rolling onto the pavement.
Paint, sometimes with additives like reflective glass beads, is generally used to mark travel lanes. It is also used to mark spaces in parking lots or special purpose spaces for handicap parking (blue), loading zones, or time restricted parking areas. Colors for these applications vary by locality.
In some areas, such as Colorado, black paint is applied on concrete before a smaller white line is painted. This improves the visibility of the white line against the "white" concrete.