Road surface marking
Road surface marking is any kind of device or material that is used on a road surface in order to convey official information; they are commonly placed with road marking machines. They can also be applied in other facilities used by vehicles to mark parking spaces or designate areas for other uses. In some countries and areas, road markings are conceived as horizontal traffic signs, as opposed to vertical traffic signs placed on posts.
Road surface markings are used on paved roadways to provide guidance and information to drivers and pedestrians. Uniformity of the markings is an important factor in minimising confusion and uncertainty about their meaning, and efforts exist to standardise such markings across borders. However, countries and areas categorise and specify road surface markings in different ways—white lines are called white lines mechanical, non-mechanical, or temporary. They can be used to delineate traffic lanes, inform motorists and pedestrians 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. Road surface marking can also indicate regulations for parking and stopping.
There is continuous effort to improve the road marking system, and technological breakthroughs include adding retroreflectivity, increasing longevity, and lowering installation cost.
Today, road markings are used to convey a range of information to the driver spanning navigational, safety and enforcement issues leading to their use in road environment understanding within advanced driver-assistance systems and consideration for future use in autonomous road vehicles.
Mechanical markers
Mechanical devices may be raised or recessed into the road surface, and either reflective or non-reflective. Most are permanent; some are movable.- Cat's eye, invented by Percy Shaw in the 1930s, cat's eyes equip many major routes in the British Isles. They consist of four reflective lenses mounted in a durable white rubber housing, two facing fore and two facing aft. The housing is mounted within a cast iron shoe, which the rubber housing sinks in to when driven over. This provides protection from snow ploughing and allows the lenses to be self-cleaning—they pass a rubber blade when depressed. The lenses are available in a variety of different colours: mainly white, yellow/orange, green, red, and blue.
- Botts' 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. 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. They are normally only used in warm climates since snow ploughs usually remove them along with the snow.
- Rumble strips are commonly used for the same purpose. A rumble strip can be a series of simple troughs, typically deep and wide, that is ground out of the asphalt. Other alternatives, similar to the Botts' dots, use raised strips, painted or glued to the surface. A specific form of raised strips using thermoplastic is called profile thermoplastic markings. The markings are created by fusing thermoplastic to the pavement and create alternating elevation and recession pattern. This can be done as inverted-profile markings or raised-profile markings. Inverted-profile markings are created by pressing a cog rolling over the markings while they are wet to make them corrugated. Raised-profile markings are created by extruding extra thickness of thermoplastic at a specific interval to create bumps. Raised-profile markings are sometime known as convex traffic lines. Uses of rumble strips can be across the travel direction or along the travel direction. Their main way of function is creating a strong vibration when driven over that will alert a driver to various upcoming hazards both by sound and the physical vibration of the vehicle. A musical road uses specific patterns of these vibrations to produce music.
- Reflective markers are used as travel lane dividers, to mark the central reservation or to mark exit slip-roads. Incorporating a raised retro-reflective element, they are typically more visible at night and in inclement weather than standard road marking lines. The colour of markers varies depending on the country of use; freeways in the United States often use reflectors manufactured to appear white to drivers proceeding in the proper direction of travel, and appear red on the reverse to warn drivers that they are proceeding against the proper direction of travel, creating a danger of a head-on collision. Reflective markers are also referred to as raised pavement markers, road studs, and sometimes in the UK and Ireland as cat's eye, although this name refers to one particular brand of product. These markers can be used for other purposes such as marking the locations of fire hydrants or at gates of gated communities to indicate that emergency service vehicles have a code or device that allows them to open the gate. In the United Kingdom and elsewhere, raised markers are used to mark pedestrian crossings to assist the blind in crossing streets. In colder climates, reflective markers may be installed below ground using an elongated narrow triangle, cut into the road surface that allows the device to be installed below the road surface. Newer technology allows these to be placed above ground with snowplough-able rails that attempt to protect the reflective components from the snowplough blade.
Confusion with marks left by roadwork
Some municipalities require contractors to install utility repair tags to identify responsible parties of the patches that fill utility cuts. The colour-coded tags are visible on the road surface.
Non-mechanical markers
Marker types
Paint
, sometimes with additives such as retroreflective glass beads, is generally used to mark travel lanes. It is also used to mark spaces in parking lots or special purpose spaces for disabled parking, loading zones, or time-restricted parking areas. Colours for these applications vary by locality. Paint is a low-cost marking and has been in widespread use since approximately the early 1950s.Paint consists of three main components: pigments, resins or binders, and water or solvents. Pigments are finely grounded materials that give out colours or block out the surface beneath it. They may contain other materials such as UV stabiliser, and fillers that bring out the colour pigments to the required level. Resins or binders are the glue of the paint to bind pigment and glass beads together to the road surface. The resins for water-based paints are polyvinyl acetate latex, methyl methacrylate or acrylic resin. The resins for solvent-based paints are linseed or soya oils and alkyd resins. The pigments and resins are mixed with water for water-based paints and solvents for solvent-based paints so that they can be applied onto the road surface. Solvents include naphtha, toluene, methanol, methylene chloride, and acetone. Due to environmental concerns, some jurisdictions may have restrictions on solvent-based paints.
Paint is usually applied right after the road has been paved. The road is marked commonly by a truck called a "striper." These trucks contain hundreds of gallons of paint stored in huge drums which sit on the bed. The markings are controlled manually or automatically by the controller who sits on the bed. Paint is run through a series of hoses under air pressure and applied to the roadway surface along with the application of glass beads for retroreflectivity. After application, the paint dries fairly quickly. Sometimes the glass beads are mixed in with the paint and applied together. However, a more recommended method is to use a separate gun to spray the glass beads on to the wet paint during the application.
Painted symbols, such as turn-lane arrows or HOV lane markers, are applied manually using stencils. Painted markings usually last 9 to 36 months. Some water-based paints can be applied at double the level of thickness of typical latex paints to extend the life of the markings.
Stones
In roads paved with setts or cobblestones, markings can be made with white blocks or stones, like marble or other light-coloured rocks. This kind of marking is long-lasting, but can be slippery in rain or wet conditions unless surfaced with a matte or rough finish.Thermoplastic
One of the most common types of road marking based on its balance between cost and performance longevity, thermoplastic binder systems are generally based on one of three core chemistries: hydrocarbons, rosin esters or maleic modified rosin esters. Thermoplastic coatings are generally homogeneous dry mixes of binder resins, plasticisers, glass beads, pigments, and fillers. Their use has increased over paints mainly due to the performance benefits of increased durability, retro-reflectivity, and a lack of VOC solvents.Thermoplastic markings are applied using specially designed vehicles. Usually, thermoplastic marking mode is applied by machine to coat traffic lines, afree preheating by a device commonly called a preheater. The thermoplastic mix is heated in trucks to about ] before being fed to the application apparatus. This is often a screed box or ribbon gun. Immediately after the thermoplastic has been applied, glass beads are laid onto the hot material so that they embed before the plastic hardens. These beads provide initial retroreflection. As the marking wears during use and the initial beads are lost, the beads mixed with the binder are uncovered, providing long-term retroreflectivity. These can be made exceptionally thick to produce a rumble strip effect.
The thermoplastic marking coating sets quickly. The melt adhesion of a synthetic resin makes hot-melt paint adhere strongly to the road surface. Additives in the coating paint increases the coating plasticity, improving the anti-settling, anti-pollution, and anti-tarnish qualities. Thermoplastic marking paint is most commonly produced in yellow and white. The white marking paint mainly contains titanium white, zinc oxide, and lithopone, while the yellow paint is mainly heat-yellowing lead.
In warm climate areas, the thermoplastic markings can last three to six years. However, snowploughs can damage the thermoplastics, limiting usage in cold-climate areas. The filling materials of road paint can affect the mechanical strength, abrasion resistance and hue of the coating film. The particle size of the paint powder influences the flow, sedimentation, and the surface processing.