Ice road on Lake Saimaa Finland

Ice roads (ice crossings, ice bridges) are frozen, human-made structures on the surface of bays, rivers, lakes, or seas in the far north. They link dry land, frozen waterways, portages and winter roads, and are usually remade each winter. Ice roads allow temporary transport to areas with no permanent road access. Seen in isolated regions of northern Canada, Alaska's Bush, northern Scandinavia and Russia, they reduce the cost of materials that otherwise would ship as expensive air freight, and they allow movement of large or heavy objects for which air freight is impractical.

Ice roads differ from winter roads in that they are built primarily across frozen waterways. Ice roads may be winter substitutes for summer ferry service. Ferry service and an ice crossing may operate yearly at the same time for several weeks.

An alternative meaning of ice bridge is a natural ice road or a structure formed during glaciation. These were used in prehistoric migration.

Function[link]

Ice road across the Mackenzie River, at Tsiigehtchic, Northwest Territories.

Because ice roads are flat, devoid of trees, rocks and other obstacles, they have a smooth driving surface. The roads from Yellowknife to Port Radium by John Denison, a pioneer of ice roads in Northern Canada from the 1950s-1970s, were largely plowed across frozen lakes, with a short overland portage between the shoreline of one lake and the next. Similar to ice roads, ice runways are common in the polar regions and include the blue ice runways such as Wilkins Runway in Antarctica or lake ice runways like Doris Lake Aerodrome in the Arctic. Ice is used as an emergency landing surface.

In general, these roads are built in areas where construction of year-round roads is expensive due to boggy muskeg land. When frozen in winter, these obstacles are easier to cross. Ice roads such as the stretch between Inuvik and Tuktoyaktuk, Northwest Territories, Canada provide an almost level driving surface with few detours several months of the year.

Ice roads and winter roads are used where year-round roads are expensive or impractical. When frozen in winter, the waterway crossings can be built up with auger holes to flood and thicken the crossing. Clearing snow (which insulates and warms) makes ice thicker, more quickly. These seasonal links last anywhere from a few weeks to several months before they become impassable.

After an ice road is plowed across a lake, the ice there gets much thicker than the surrounding lake ice, because the snow cover is swept off — exposing the road directly to subfreezing air (temperatures as low as −50 °C (−58 °F)). When a lake thaws in the spring, the ice under the road is the last to melt, and in the summer, traces of the roads can still be seen from overhead in a bush plane, as bare strips remain on the lake floor where the ice blocked light and prevented plants and algae from growing.

Driving[link]

Vehicles crossing the Albany River on the winter road running from Moosonee to Attawapiskat in Northern Ontario, Canada. Edge of road is marked by small trees. Heavy vehicles must maintain wide spacing and low speeds.

While easier to drive across in the winter than land, roads over water present a great danger to anyone using them. Speeds are typically limited to 25 km/h (16 mph) to prevent a truck's weight from causing waves under the surface. These waves can damage the road, or dislodge the ice from the shoreline and create a hazard. Another hazard on large lakes is the pressure ridge, a break in the ice created by the expansion and contraction of the surface ice due to heat.

The roads are normally the domain of large trucks (e.g. tractor-trailer units), although lighter vehicles, such as pickup trucks, are occasionally seen, as are snowmobiles.

Use of ice as the main construction material allows unusual construction techniques: to make a ramp to get the road over a step such as the shore of a lake, for example, lake water is pumped out and mixed with snow to make slush, formed into the shape of the ramp, and allowed to quickly freeze in the intense cold. Worn and damaged roads are repaired by flooding with shallow water that freezes into a new surface layer.^[1]

Around the world[link]

Antarctica[link]

Cargo caravan on the South Pole Traverse early 2006

The South Pole Traverse (McMurdo-South Pole highway) is approximately 1,400 km (870 mi) long and links the United States' McMurdo Station on the coast to the Amundsen–Scott South Pole Station. It was constructed by leveling snow and filling in crevasses, but is not paved. There are flags to mark the route.

Canada[link]

Some of the first ice roads in history were built in the 1930s in northern Canada, for use by caterpillar sleds pulling heavy loads called tractor trains for mines where loads were too heavy for transport by aircraft and the soil too boggy for standard roads when the land was not frozen.^[2] Winter roads and ice roads in Canada are found primarily in northern parts of some provinces, as well as the sparsely-populated northern territories of Yukon, Northwest Territories and Nunavut. In Nunavut, while there are a number of permanent roads within the territory, the Tibbitt to Contwoyto Winter Road, linking Nunavut to Tibbitt Lake in the Northwest Territories, forms the territory's only road access to the rest of North America's road network.

Ice road on Great Slave Lake

Winter roads in the Northwest Territories, most notably the Tuktoyaktuk Winter Road, link various isolated communities and mineral exploration sites to the territory's highway network.

Winter roads may also be found in the sparsely populated northernmost regions of some Canadian provinces. Most communities north of Ontario's Albany River are served by winter roads. Most of these roads in Northwestern Ontario are linked to the Northern Ontario Resource Trail, a permanent gravel road which extends northerly from the end of Highway 599 at Pickle Lake, the northernmost community in the province with year-round highway access. In Northeastern Ontario, some communities are linked to Moosonee, a town that has rail access but no road access to the south.

Estonia[link]

The Estonian Road Administration is responsible for managing ice roads in winter. An ice road may be opened when ice thickness is at least 22 cm (8.7 in) along the entire route. An ice road to Piirissaar Island in Lake Peipus is opened in most years, while colder winters permit opening official ice roads on the Baltic Sea between mainland Estonia and the islands of Hiiumaa, Vormsi, Muhu and Kihnu, between the islands of Saaremaa and Hiiumaa and also between Haapsalu and Noarootsi. As of 2011, the longest ice road in Europe is the 26.5 km route between Rohuküla on the continent and Heltermaa in Hiiumaa.^[3] The limitations for ice road traffic include:

Ice road between Hiiumaa and mainland Estonia in 2003.

• Weight limit depending on conditions, mostly 2 t (2.0 long tons; 2.2 short tons) to 2.5 t (2.5 long tons; 2.8 short tons)
• Vehicles travelling in the same direction must be at least 250 m (820 ft) apart.
• Recommended travelling speeds are under 25 km/h (16 mph) or between 40–70 km/h (25–43 mph). It is advised to avoid the range of 25 and 40 km/h (16 and 25 mph) due to danger of creating resonance in the ice layer (i.e. vehicle speed and water wave speed being the same or nearly, resulting in a large wave under the ice that breaks the ice).
• Seat belts must not be fastened due to danger of drowning if the ice breaks.
• The vehicle must not be stopped.
• Vehicles are allowed to enter the ice road in three minute intervals.
• Ice roads may only be used in daylight.

Ice road lengths:

• Virtsu - Kuivastu (between the mainland and Muhu) - 9.0 km
• Rohuküla - Heltermaa (between the mainland and Hiiumaa) - 26.5 km
• Rohuküla - Sviby (between the mainland and Vormsi) - 10.2 km
• Tärkma - Triigi^{[disambiguation needed ]} (between Hiiumaa and Saaremaa) - 14.5 km
• Haapsalu - Noarootsi - 3.2 km
• Lao - Kihnu (between the mainland and Kihnu) - 13.0 km

Finland[link]

Tractor with a snowblower on Kallavesi in Kuopio

The Finnish Road Administration maintains some ice roads during winters. These roads are considered as public roads when they are open. The longest 7 km (4.3 mi) road crosses Lake Pielinen.^[4] Ice must be at least 40 cm (16 in) thick before the road may be opened. The following limits apply to ice roads:

• Weight limit 3 t (3.0 long tons; 3.3 short tons) (may be raised if ice is thick enough)
• Speed limit 50 km/h (31 mph)
• Minimum space of 50 m (164 ft) between cars traveling in the same direction
• Overtaking is prohibited.
• Stopping is prohibited.

On the severest winters ice roads have been privately constructed from the mainland of Finland to the Åland Islands and elsewhere in the Archipelago; using these is unlikely to be within any insurance policy.

Norway[link]

Over the Tana river there are usually two ice roads from December to April. These roads have a weight limit of 2 t (2.0 long tons; 2.2 short tons), but few other limitations. There are numerous ice roads over frozen rivers elsewhere in Norway.^[specify]

Sweden[link]

In the northern part of Sweden are many ice roads. Vägverket maintains them, but some private ice roads also exist. Ice roads are usually put in when ice thickness exceeds 20 cm (7.9 in). The limitations for ice road traffic normally include:

• A speed limit of 30 km/h (19 mph).
• Prohibition against stopping or parking on the ice.
• Minimum distance of 50 m (160 ft) between vehicles.
• Restrictions for axle, bogie and gross weight.

The longest ice road 15 km (9.3 mi) in Sweden is in the Luleå Archipelago, Bothnian Bay (in the northernmost part of the Gulf of Bothnia). It starts in the port of Hindersöstallarna and connects the islands Hindersön, Stor-Brändön, and Långön with the mainland. The ice roads in Luleå are usually open from January to April and have a weight restriction of 2–4 t (2.0–3.9 long tons; 2.2–4.4 short tons).

There are several ice roads across the lake Storsjön. The roads are usually open from January to April and have a weight restriction of 2–4 t (2.0–3.9 long tons; 2.2–4.4 short tons).

The southernmost ice road in Sweden is on lake Hjälmaren, to Vinön island.^[5] Due to poor ice it is not open every season.

Russia[link]

An example of an ice road was the Road of Life across the frozen Lake Ladoga, which provided the only access to the besieged city of Leningrad in the winter months during World War II.

The Lena River has an ice road on its surface for hundreds of kilometres during the winter.

United States[link]

There is an ice road in the United States on Lake Superior, linking the city of Bayfield, Wisconsin on the mainland with La Pointe, Wisconsin on Madeline Island. The road is about 3 km (1.9 mi) long and is used for several weeks in the year as replacement for the summer ferry service. When the ice is too thin to allow the construction of the road, but too thick to allow ferry service, a type of hovercraft is used to transport school children from the island to and from the mainland.^[6] In Michigan's Straits of Mackinac, seasonal ice roads also connect Mackinac Island and Bois Blanc Island with the mainland.

In Prudhoe Bay in Alaska, there is an ice road over the Arctic Ocean about 40 km (25 mi) long and its maximum speed is 10 mph (16 km/h). It is used a few months during winter to serve an oil field site on the ocean. Another ice road in Alaska is the ice road from Prudhoe Bay, Alaska to Point Thomson, Alaska. The ice road is 110 km (68 mi) long and is on the Beaufort Sea; this ice road is mainly used by semi-trucks to deliver loads to serve the Point Thomson area.

There is a seasonal ice road constructed from the Kuparuk Oil Field to the Alpine oil field, which is roadless in the summer months. This road also connects to the village of Nuiqsut, on the banks of the Colville River. This road is roughly 50 km (31 mi) long and is used to resupply Alpine with critical supplies for operations as well as to transport drilling rigs.

Media references[link]

Ice road across a branch of the Amur River, some 40 km NE of Khabarovsk

The 2008 film Frozen River tells the story of two women who get involved with trafficking illegal immigrants from Canada into the United States by driving them across the frozen St. Lawrence River in their car.

Canada's ice roads were prominently featured in the History Channel show Ice Road Truckers.

See also[link]

• Ice pier
• ice racing

References[link]

External links[link]

Wikimedia Commons has media related to: Ice roads

• Government of NWT Department of Transportation - Ice Roads / Ice Bridges / Winter Roads
• Government of NWT Highway Condition Reports
• Building Canada's Epic Ice Road, Popular Mechanics article.
• 1959 John Denison's Ice Roads NWT Historical Timeline, Prince of Wales Northern Heritage Centre

A natural block of (water) ice

Snowflakes (ice crystals) by Wilson Bentley, 1902

Ice is water frozen into the solid state. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions. The addition of other materials such as soil may further alter the appearance.

Ice appears in nature in forms of snowflakes, hail, icicles, glaciers, pack ice, and entire polar ice caps. It is an important component of the global climate, and plays an important role in the water cycle. Furthermore, ice has numerous cultural applications, from ice cooling of drinks to winter sports and the art of ice sculpting.

The molecules in solid ice may be arranged in different ways, called phases, depending on the temperature and pressure. Usually ice is the phase known as ice I_h, which is the most abundant of the varying solid phases on the Earth's surface. The most common phase transition to ice I_h occurs when liquid water is cooled below 0°C (273.15K, 32°F) at standard atmospheric pressure. It can also deposit from vapour with no intervening liquid phase, such as in the formation of frost.

The word is derived from Old English īs, which in turn stems from Proto-Germanic isaz.

Characteristics[link]

Crystal structure of hexagonal ice. Grey dashed lines indicate hydrogen bonds.

As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered a mineral.^[1] It possesses a regular crystalline structure based on the molecule of water, which consists of a single oxygen atom covalently bonded to two hydrogen atoms, or H-O-H. However, many of the physical properties of water and ice are controlled by the formation of hydrogen bonds between adjacent oxygen and hydrogen atoms. It is a weak bond, but is critical in controlling the structure of both water and ice.

An unusual property of ice frozen at atmospheric pressure is that the solid is approximately 8.3% less dense than liquid water. The density of ice is 0.9167 g/cm³ at 0 °C, whereas water has a density of 0.9998 g/cm³ at the same temperature. Liquid water is densest, essentially 1.00 g/cm³, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals^[2] of ice as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid. Density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm³ at −180 °C (93 K).^[3]

The effect of expansion during freezing can be dramatic, and is a basic cause of freeze-thaw weathering of rock in nature. It is also a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes, then leak water after thawing.

The result of this process is that ice (in its most common form) floats on liquid water, which is an important feature in Earth's biosphere. It has been argued that without this property natural bodies of water would freeze, in some cases permanently, from the bottom up,^[4] resulting in a loss of bottom-dependent animal and plant life in fresh and sea water. Sufficiently thin ice sheets allow light to pass through while protecting the underside from short-term weather extremes such as wind chill. This creates a sheltered environment for bacterial and algal colonies. When sea water freezes, the ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae, copepods and annelids, which in turn provide food for animals such as krill and specialised fish like the Bald notothen, fed upon in turn by larger animals such as Emperor penguins and Minke whales.^[5]

When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C. During the melting process, the temperature remains constant at 0 °C. While melting, any energy added breaks the hydrogen bonds between ice (water) molecules. Energy becomes available to increase the thermal energy (temperature) only after enough hydrogen bonds are broken that the ice can be considered liquid water. The amount of energy consumed in breaking hydrogen bonds in the transition from ice to water is known as the heat of fusion.

As with water, ice absorbs light at the red end of the spectrum preferentially as the result of an overtone of an oxygen-hydrogen (O-H) bond stretch. Compared with water, this absorption is shifted toward slightly lower energies. Thus, ice appears blue, with a slightly greener tint than for liquid water. Since absorption is cumulative, the color effect intensifies with increasing thickness or if internal reflections cause the light to take a longer path through the ice.^[6]

Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than the ice itself. For instance, icebergs containing impurities (e.g., sediments, algae, air bubbles) can appear brown, grey or green.^[6]

Slipperiness[link]

Frozen waterfall in southeast New York

It has long been believed that ice is slippery because the pressure of an object in contact with it causes a thin layer to melt. For example, the blade of an ice skate, exerting pressure on the ice, melts a thin layer, providing lubrication between the ice and the blade. This explanation, called "pressure melting", originated in 19th century. This however did not account for skating on ice temperatures lower than -3.5 °C, whereas skaters often skate on lower temperature ice. In 20th century an alternative explanation, called "friction heating" was proposed, whereby friction of the material was causing the ice layer melting. However, this theory also failed to explain skating at low temperature. In fact, neither explanation explained why ice is slippery when standing still even at below-zero temperatures.^[7]

This explanation has come into doubt with the proposal that ice molecules in contact with air cannot properly bond with the molecules of the mass of ice beneath (and thus are free to move like molecules of liquid water). These molecules remain in a semiliquid state, providing lubrication regardless of pressure against the ice exerted by any object.^[8]

Formation[link]

Feather ice on the plateau near Alta, Norway. The crystals form at temperatures below −30 °C (i.e. −22 °F).

Ice that is found at sea may be in the form of sea ice, pack ice, or icebergs. The term that collectively describes all of the parts of the Earth's surface where water is in frozen form is the cryosphere. Ice is an important component of the global climate, particularly in regard to the water cycle. Glaciers and snowpacks are an important storage mechanism for fresh water; over time, they may sublimate or melt. Snowmelt is often an important source of seasonal fresh water.

Rime is a type of ice formed on cold objects when drops of water crystallize on them. This can be observed in foggy weather, when the temperature drops during the night. Soft rime contains a high proportion of trapped air, making it appear white rather than transparent, and giving it a density about one quarter of that of pure ice. Hard rime is comparatively denser.

Aufeis is layered ice that forms in Arctic and subarctic stream valleys. Ice, frozen in the stream bed, blocks normal groundwater discharge, and causes the local water table to rise, resulting in water discharge on top of the frozen layer. This water then freezes, causing the water table to rise further and repeat the cycle. The result is a stratified ice deposit, often several meters thick.

Ice can also form icicles, similar to stalactites in appearance, or stalagmite-like forms as water drips and re-freezes.

Clathrate hydrates are forms of ice that contain gas molecules trapped within its crystal lattice.

Pancake ice is a formation of ice generally created in areas with less calm conditions.

Candle Ice is a form of Rotten Ice that develops in columns perpendicular to the surface of a lake.

Ice discs are circular formations of ice surrounded by water in a river.

The World Meteorological Organization defines several kinds of ice depending on origin, size, shape, influence and so on.^[9]

Ice pellets[link]

An accumulation of ice pellets

Ice pellets are a form of precipitation consisting of small, translucent balls of ice. This form of precipitation is also known as sleet.^[10] Ice pellets are usually (but not always) smaller than hailstones.^[11] They often bounce when they hit the ground, and generally do not freeze into a solid mass unless mixed with freezing rain. The METAR code for ice pellets is PL.^[12]

Ice pellets form when a layer of above-freezing air is located between 1,500 metres (4,900 ft) and 3,000 metres (9,800 ft) above the ground, with sub-freezing air both above and below it. This causes the partial or complete melting of any snowflakes falling through the warm layer. As they fall back into the sub-freezing layer closer to the surface, they re-freeze into ice pellets. However, if the sub-freezing layer beneath the warm layer is too small, the precipitation will not have time to re-freeze, and freezing rain will be the result at the surface. A temperature profile showing a warm layer above the ground is most likely to be found in advance of a warm front during the cold season,^[13] but can occasionally be found behind a passing cold front.

Hail[link]

A large hailstone, about 6 cm (2.36 in) in diameter

Like other precipitation, hail forms in storm clouds when supercooled water droplets freeze on contact with condensation nuclei, such as dust or dirt. The storm's updraft blows the hailstones to the upper part of the cloud. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. Hail has a diameter of 5 millimetres (0.20 in) or more.^[14] Within METAR code, GR is used to indicate larger hail, of a diameter of at least 6.4 millimetres (0.25 in). GR is derived from the French word grêle. Smaller-sized hail, as well as snow pellets, use the coding of GS, which is short for the French word grésil.^[12] Stones just larger than golf ball-sized are one of the most frequently reported hail sizes.^[15] Hailstones can grow to 15 centimetres (6 in) and weigh more than .5 kilograms (1.1 lb).^[16] In large hailstones, latent heat released by further freezing may melt the outer shell of the hailstone. The hailstone then may undergo 'wet growth', where the liquid outer shell collects other smaller hailstones.^[17] The hailstone gains an ice layer and grows increasingly larger with each ascent. Once a hailstone becomes too heavy to be supported by the storm's updraft, it falls from the cloud.^[18]

Hail forms in strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing 0 °C (32 °F).^[14] Hail-producing clouds are often identifiable by their green coloration.^[19][20] The growth rate is maximized at about −13 °C (9 °F), and becomes vanishingly small much below −30 °C (−22 °F) as supercooled water droplets become rare. For this reason, hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of 11,000 feet (3,400 m).^[21] Entrainment of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes because the atmosphere over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations.^[22]

Snowflakes[link]

Snowflake viewed in an optical microscope

Snow crystals form when tiny supercooled cloud droplets (about 10 μm in diameter) freeze. These droplets are able to remain liquid at temperatures lower than −18 °C (255 K; −0 °F), because to freeze, a few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice; then the droplet freezes around this "nucleus." Experiments show that this "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than −35 °C (238 K; −31 °F).^[23] In warmer clouds an aerosol particle or "ice nucleus" must be present in (or in contact with) the droplet to act as a nucleus. Our understanding of what particles make efficient ice nuclei is poor — what we do know is they are very rare compared to that cloud condensation nuclei on which liquid droplets form. Clays, desert dust and biological particles may be effective,^[24] although to what extent is unclear. Artificial nuclei include particles of silver iodide and dry ice, and these are used to stimulate precipitation in cloud seeding.^[25]

Once a droplet has frozen, it grows in the water-supersaturated air, when the temperature remains below the freezing point. The droplet then grows by condensation of water vapor onto the ice surfaces. Air saturation with water is maintained by continuous simultaneous evaporation of water droplets. Thus ice crystals grow at the expense of water droplets in a process called the Wegner-Bergeron-Findeison process. These large crystals are an efficient source of precipitation, since they fall through the atmosphere due to their weight, and may collide and aggregate in clusters. These aggregates are snowflakes, and are usually the type of ice particle that falls to the ground.^[26] Guinness World Records list the world’s largest snowflakes as those of January 1887 at Fort Keogh, Montana; allegedly one measured 38 cm (15 inches) wide.^[27]

The exact details of the sticking mechanism remain controversial. Possibilities include mechanical interlocking, sintering, electrostatic attraction as well as the existence of a "sticky" liquid-like layer on the crystal surface. The individual ice crystals often have hexagonal symmetry. Although the ice is clear, scattering of light by the crystal facets and hollows/imperfections mean that the crystals often appear white in color due to diffuse reflection of the whole spectrum of light by the small ice particles.^[28] The shape of the snowflake is determined broadly by the temperature and humidity at which it is formed.^[26] Rarely, at a temperature of around −2 °C (28 °F), snowflakes can form in threefold symmetry — triangular snowflakes.^[29] The most common snow particles are visibly irregular, although near-perfect snowflakes may be more common in pictures because they are more visually appealing. It is unlikely that any two snowflakes are alike due to the estimated 10¹⁹ (10 quintillion) water molecules which make up a typical snowflake,^[30] which grow at different rates and in different patterns depending on the changing temperature and humidity within the atmosphere that the snowflake falls through on its way to the ground.^[31] The METAR code for snow is SN, while snow showers are coded SHSN.^[12]

Diamond dust[link]

Diamond dust, also known as ice needles or ice crystals, forms at temperatures approaching −40 °F (−40 °C) due to air with slightly higher moisture from aloft mixing with colder, surface based air.^[32] The METAR identifier for diamond dust within international hourly weather reports is IC.^[12]

Production[link]

Harvesting ice on Lake Saint Clair in Michigan, c. 1905

B&W film of 1919 ice harvest at Pocono Manor in the Poconos

An ice manufacturing plant in East Midnapore, India

Ice is now mechanically produced on a large scale, but before refrigeration was developed ice was harvested from natural sources for human use.

Ice harvesting[link]

Ice has long been valued as a means of cooling. In 400 BC Iran, Persian engineers had already mastered the technique of storing ice in the middle of summer in the desert. The ice was brought in during the winters from nearby mountains in bulk amounts, and stored in specially designed, naturally cooled refrigerators, called yakhchal (meaning ice storage). This was a large underground space (up to 5000 m³) that had thick walls (at least two meters at the base) made out of a special mortar called sārooj, composed of sand, clay, egg whites, lime, goat hair, and ash in specific proportions, and which was known to be resistant to heat transfer. This mixture was thought to be completely water impenetrable. The space often had access to a Qanat, and often contained a system of windcatchers which could easily bring temperatures inside the space down to frigid levels on summer days. The ice was used to chill treats for royalty.

There were thriving industries in the 16/17th century in UK whereby low lying areas along the River Thames estuary were flooded during the winter, and ice harvested in carts and stored inter-seasonally in insulated wooden houses as a provision to an icehouse often located in large country houses, and widely used to keep fish fresh when caught in distant waters. This was copied from the Chinese who had been doing it for thousands of years. This was reportedly copied by an Englishman who had seen the same activity in China.^[33] Ice was imported into England from Norway on a considerable scale as early as 1823.^[34]

In the United States, the first cargo of ice was sent from New York City to Charleston, South Carolina in 1799,^[34] and by the first half of the 19th century, ice harvesting had become big business. Frederic Tudor, who became known as the “Ice King,” worked on developing better insulation products for the long distance shipment of ice, especially to the tropics; this became known as the ice trade.

Triest sent ice to Egypt, Corfu, and Zante; Switzerland sent it to France; and Germany sometimes was supplied from Bavarian lakes.^[34]

Until recently,^[when?] the Hungarian Parliament building used ice harvested in the winter from Lake Balaton for air conditioning. Icehouses were used to store ice formed in the winter, to make ice available all year long, and early refrigerators were known as iceboxes, because they had a block of ice in them. In many cities, it was not unusual to have a regular ice delivery service during the summer. The advent of artificial refrigeration technology has since made delivery of ice obsolete.

Ice harvesting is still done for ice and snow sculpture events. A swing saw is used to get ice out of the river for the Harbin International Ice and Snow Sculpture Festival each year. A swing saws is used to cut ice out from the frozen surface of the Songhua River.^[35] Many ice sculptures are made from the ice.

Commercial production[link]

Ice is now produced on an industrial scale, for uses including food storage and processing, chemical manufacturing, concrete mixing and curing, and consumer or packaged ice.^[36] Most commercial ice makers produce three basic types of fragmentary ice: flake, tubular and plate, using a variety of techniques.^[36] Large batch ice makers can produce up to 75 tons of ice per day.^[37]

Ice production is a large business; in 2002, there were 426 commercial ice-making companies in the United States, with a combined value of shipments of $595,487,000.^[38]

For small-scale ice production, many modern home refrigerators can also make ice with a built in icemaker, which will typically make ice cubes or crushed ice. Stand-alone icemaker units that make ice cubes are often called ice machines.

Uses[link]

Sports[link]

Ice sailing on the Żnin Small Lake

Ice also plays a central role in winter recreation and in many sports such as ice skating, tour skating, ice hockey, ice fishing, ice climbing, curling, broomball and sled racing on bobsled, luge and skeleton. Many of the different sports played on ice get international attention every four years during the Winter Olympic Games.

A sort of sailboat on blades gives rise to ice yachting. The human quest for excitement has even led to ice racing, where drivers must speed on lake ice, while also controlling the skid of their vehicle (similar in some ways to dirt track racing). The sport has even been modified for ice rinks.

Other uses[link]

• Ice cubes or crushed ice can be used to cool drinks. As the ice melts, it absorbs heat and keeps the drink near 0 °C (32 °F).
• Ice can be used to reduce swelling (by decreasing blood flow) and pain by pressing it against an area of the body.^[39]

Ice pier during 1983 cargo operations. McMurdo Station, Antarctica

• Engineers used formidable strength of pack ice when they constructed Antarctica's first floating ice pier in 1973.^[40] Such ice piers are used during cargo operations to load and offload ships. Fleet operations personnel make the floating pier during the winter. They build upon naturally-occurring frozen seawater in McMurdo Sound until the dock reaches a depth of about 22 feet (6.7 m). Ice piers have a lifespan of three to five years.
• Structures and ice sculptures are built out of large chunks of ice. The structures are mostly ornamental (as in the case with ice castles), and not practical for long-term habitation. Ice hotels exist on a seasonal basis in a few cold areas. Igloos are another example of a temporary structure, made primarily from snow.
• During World War II, Project Habbakuk was a British programme which investigated the use of pykrete (wood fibers mixed with ice) as a possible material for warships, especially aircraft carriers, due to the ease with which a large deck could be constructed, but the idea was given up when there were not enough funds for construction of a prototype.
• Ice can be used to start a fire by carving it into a lens which will focus sunlight onto kindling. A fire will eventually start.^[41]
• Ice has even been used as the material for a variety of musical instruments, for example by percussionist Terje Isungset.^[42]
• Ice was once used to cool refrigerators in the 19th century, which is reflected in the name "iceboxes."
• Ice can be used to store cooling, which has the same effect as storing electricity Thermal energy storageAir conditioning

Ice and transportation[link]

U.S. Coast Guard icebreakers near McMurdo Station, February 2002

Ice can also be an obstacle; for harbors near the poles, being ice-free is an important advantage; ideally, all year long. Examples are Murmansk (Russia), Petsamo (Russia, formerly Finland) and Vardø (Norway). Harbors which are not ice-free are opened up using icebreakers.

Ice forming on roads is a dangerous winter hazard. Black ice is very difficult to see, because it lacks the expected frosty surface. Whenever there is freezing rain or snow which occurs at a temperature near the melting point, it is common for ice to build up on the windows of vehicles. Driving safely requires the removal of the ice build-up. Ice scrapers are tools designed to break the ice free and clear the windows, though removing the ice can be a long and laborious process.

Far enough below the freezing point, a thin layer of ice crystals can form on the inside surface of windows. This usually happens when a vehicle has been left alone after being driven for a while, but can happen while driving, if the outside temperature is low enough. Moisture from the driver's breath is the source of water for the crystals. It is troublesome to remove this form of ice, so people often open their windows slightly when the vehicle is parked in order to let the moisture dissipate, and it is now common for cars to have rear-window defrosters to solve the problem. A similar problem can happen in homes, which is one reason why many colder regions require double-pane windows for insulation.

When the outdoor temperature stays below freezing for extended periods, very thick layers of ice can form on lakes and other bodies of water, although places with flowing water require much colder temperatures. The ice can become thick enough to drive onto with automobiles and trucks. Doing this safely requires a thickness of at least 30 cm (one foot).

For ships, ice presents two distinct hazards. Spray and freezing rain can produce an ice build-up on the superstructure of a vessel sufficient to make it unstable, and to require it to be hacked off or melted with steam hoses. And icebergs — large masses of ice floating in water (typically created when glaciers reach the sea) — can be dangerous if struck by a ship when underway. Icebergs have been responsible for the sinking of many ships, the most famous probably being the Titanic.

Ice formation on window glass of high altitude flying airplane

For aircraft, ice can cause a number of dangers. As an aircraft climbs, it passes through air layers of different temperature and humidity, some of which may be conducive to ice formation. If ice forms on the wings or control surfaces, this may adversely affect the flying qualities of the aircraft. During the first non-stop flight of the Atlantic, the British aviators Captain John Alcock and Lieutenant Arthur Whitten Brown encountered such icing conditions – Brown left the cockpit and climbed onto the wing several times to remove ice which was covering the engine air intakes of the Vickers Vimy aircraft they were flying.

A particular icing vulnerability associated with reciprocating internal combustion engines is the carburetor. As air is sucked through the carburetor into the engine, the local air pressure is lowered, which causes adiabatic cooling. So, in humid near-freezing conditions, the carburetor will be colder, and tend to ice up. This will block the supply of air to the engine, and cause it to fail. For this reason, aircraft reciprocating engines with carburetors are provided with carburetor air intake heaters. The increasing use of fuel injection—which does not require carburetors—has made "carb icing" less of an issue for reciprocating engines.

Jet engines do not experience carb icing, but recent evidence indicates that they can be slowed, stopped, or damaged by internal icing in certain types of atmospheric conditions much more easily than previously believed. In most cases, the engines can be quickly restarted and flights are not endangered, but research continues to determine the exact conditions which produce this type of icing, and find the best methods to prevent, or reverse it, in flight.

Phases[link]

Ice may be any one of the 15 known solid phases of water.

Most liquids freeze at a higher temperature under pressure, because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: water freezes at a temperature below 0 °C under a pressure higher than 1 atm (0.10 MPa). Consequently, water also remains frozen at a temperature above 0 °C under a pressure lower than 1 atm. The melting of ice under high pressures is thought to contribute to the movement of glaciers.

Ice, water, and water vapour can coexist at the triple point, which is exactly 0.01 °C or 273.16 K (by definition) at a pressure of 611.73 Pa. Unlike most other solids, ice is difficult to superheat. In an experiment ice at −3 °C was superheated to about 17 °C for about 250 picoseconds.^[43]

Subjected to higher pressures and varying temperatures, ice can form in fifteen separate known phases. With care all these phases except ice X can be recovered at ambient pressure and low temperature. The types are differentiated by their crystalline structure, ordering and density. There are also two metastable phases of ice under pressure, both fully hydrogen-disordered; these are IV and XII. Ice XII was discovered in 1996. In 2006, XIII and XIV were discovered.^[44] Ices XI, XIII, and XIV are hydrogen-ordered forms of ices I_h, V, and XII respectively. In 2009, ice XV was found at extremely high pressures and −143 °C.^[45] At even higher pressures, ice is predicted to become a metal; this has been variously estimated to occur at 1.55 TPa^[46] or 5.62 TPa.^[47]

As well as crystalline forms, solid water can exist in amorphous states as amorphous solid water (ASW), low-density amorphous ice (LDA), high-density amorphous ice (HDA), very high-density amorphous ice (VHDA) and hyperquenched glassy water (HGW).

In outer space, hexagonal crystalline ice (the predominant form found on Earth) is extremely rare. Amorphous ice is more common; however, hexagonal crystalline ice can be formed via volcanic action.^[48]

Log-lin pressure-temperature phase diagram of water. The Roman numerals correspond to some ice phases listed below.

Other ices[link]

Detail of an ice cube

The solid phases of several other volatile substances are also referred to as ices; generally a volatile is classed as an ice if its melting point lies above ~100 K. The best known example is dry ice, the solid form of carbon dioxide.

A "magnetic analogue" of ice is also realized in some insulating magnetic materials in which the magnetic moments mimic the position of protons in water ice and obey energetic constraints similar to the Bernal-Fowler ice rules arising from the geometrical frustration of the proton configuration in water ice. These materials are called spin ice.

See also[link]

• Density of ice versus water
• Ice famine
• Pumpable ice technology

References[link]

External links[link]

Look up ice in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Ice

• The National Snow and Ice Data Center, based in the United States
• The phase diagram of water, including the ice variants
• Webmineral listing for Ice
• MinDat.org listing and location data for Ice
• The physics of ice
• The phase diagrams of water with some high pressure diagrams
• 'Unfreezable' water, 'bound water' and water of hydration
• Electromechanical properties of ice
• Estimating the maximum thickness of an ice layer
• Sandia's Z machine creates ice in nanoseconds
• Amazing ice at Lac Leman
• The Surprisingly Cool History of Ice

A road is a route, thoroughfare or way that supports travel by a means of conveyance.

Definitions[link]

For purposes of international statistical comparison, the Organisation for Economic Co-operation and Development (OECD) defines a road as "a line of communication (travelled way) using a stabilized base other than rails or air strips open to public traffic, primarily for the use of road motor vehicles running on their own wheels," which includes "bridges, tunnels, supporting structures, junctions, crossings, interchanges, and toll roads, but not cycle paths."^[1] In urban areas roads may diverge through a city or village and be named as streets, serving a dual function as urban space easement and route.^[2] Modern roads are normally smoothed, paved, or otherwise prepared to allow easy travel.^[3] Historically many roads were simply recognizable routes without any formal construction or maintenance.^[4]

United States[link]

In the United States, laws distinguish between public roads, which are open to public use, and private roads, which are privately controlled.^[5]

United Kingdom[link]

In the United Kingdom there is some ambiguity between the terms highway and road. The Highway code details rules for "road users".^[6] For the purposes of the English law, Highways Act 1980, which covers England and Wales but not Scotland or Northern Ireland, the term road is defined to be "any length of highway or of any other road to which the public has access, and includes bridges over which a road passes."^[7] This includes footpaths, bridleways and cycle tracks, and also road and driveways on private land and many car parks.^[8] Vehicle Excise Duty, a road use tax, is payable on some vehicles used on the public road.^[8]

The definition of a road depends on the definition of a highway, however there is no formal definition for a highway in the relevant Act. A 1984 ruling said "the land over which a public right of way exists is known as a highway; and although most highways have been made up into roads, and most easements of way exist over footpaths, the presence or absence of a made road has nothing to do with the distinction.^[9][10] Another legal view is that while a highway historically included footpaths, bridleways, driftways, etc., it can now be used to mean those ways that allow the movement of motor-vehicles, and the term rights of way can be used to cover the wider usage.^[11]

Historical road construction[link]

The Porta Rosa is a Greek street dating from the 3rd to 4th century BC in Velia, Italy with a paved surface and gutters.

A paved Roman road in Pompeii, Italy

The assertion that the first pathways were the trails made by animals has not been universally accepted, since in many cases animals do not follow constant paths.^[4] Others believe that some roads originated from following animal trails.^[12][13] The Icknield Way is given as an example of this type of road origination, where man and animal both selected the same natural line.^[14] By about 10,000 BC, rough pathways were used by human travelers.^[4]

• The world's oldest known paved road was laid in Egypt some time between 2600 and 2200 BC.^[15]

• Stone-paved streets are found in the city of Ur in the Middle East dating back to 4000 BC.^[4]

• Corduroy roads (log roads) are found dating to 4000 BC in Glastonbury, England.^[4]

• The timber trackway; Sweet Track causeway in England, is one of the oldest engineered roads discovered and the oldest timber trackway discovered in Northern Europe. Built in winter 3807 BC or spring 3806 BC, tree-ring dating (Dendrochronology) enabled very precise dating. It has been claimed to be the oldest road in the world.^[16][17]

• Brick-paved streets were used in India as early as 3000 BC .^[4]

• In 500 BC, Darius I the Great started an extensive road system for Persia (Iran), including the famous Royal Road, which was one of the finest highways of its time.^[18] The road remained in use after Roman times.

• In ancient times, transport by river was far easier and faster than transport by road,^[17] especially considering the cost of road construction and the difference in carrying capacity between carts and river barges. A hybrid of road transport and ship transport beginning in about 1740 is the horse-drawn boat in which the horse follows a cleared path along the river bank.^[19][20]

• From about 312 BC, the Roman Empire built straight^[21] strong stone Roman roads throughout Europe and North Africa, in support of its military campaigns. At its peak the Roman Empire was connected by 29 major roads moving out from Rome and covering 78,000 kilometers or 52,964 Roman miles of paved roads.^[17]

• In the 8th century AD, many roads were built throughout the Arab Empire. The most sophisticated roads were those in Baghdad, Iraq, which were paved with tar. Tar was derived from petroleum, accessed from oil fields in the region, through the chemical process of destructive distillation.^[22]

• The Highways Act 1555 in Britain transferred responsibility for maintaining roads from government to local parishes.^[17] This resulted in a poor and variable state of roads. To remedy this, the first of the "Turnpike trusts" was established around 1706, to build good roads and collect tolls from passing vehicles. Eventually there were approximately 1,100 trusts in Britain and some 36,800 km (22,870 miles) of engineered roads.^[17] The Rebecca Riots in Carmarthenshire and Rhayader from 1839 to 1844 contributed to a Royal Commission that led to the demise of the system in 1844,^[23] which coincided with the development of the UK railway system.

Design[link]

Structural road design is the science of designing a road for its environment in order to extend its longevity and reduce maintenance. The Shell pavement design method is used in many countries for the design of new asphalt roads.

Construction[link]

A road being torn up.

Surveyor at work with a leveling instrument.

Asphalt layer and roller

Road construction requires the creation of a continuous right-of-way, overcoming geographic obstacles and having grades low enough to permit vehicle or foot travel.^{[24] (pg15)} and may be required to meet standards set by law^[25] or official guidelines.^[26] The process is often begun with the removal of earth and rock by digging or blasting, construction of embankments, bridges and tunnels, and removal of vegetation (this may involve deforestation) and followed by the laying of pavement material. A variety of road building equipment is employed in road building.^[27][28]

After design, approval, planning, legal and environmental considerations have been addressed alignment of the road is set out by a surveyor.^[21] The Radii and gradient are designed and staked out to best suit the natural ground levels and minimize the amount of cut and fill.^{[26] (page34)} Great care is taken to preserve reference Benchmarks ^{[26] (page59)}

Roads are designed and built for primary use by vehicular and pedestrian traffic. Storm drainage and environmental considerations are a major concern. Erosion and sediment controls are constructed to prevent detrimental effects. Drainage lines are laid with sealed joints in the road easement with runoff coefficients and characteristics adequate for the land zoning and storm water system. Drainage systems must be capable of carrying the ultimate design flow from the upstream catchment with approval for the outfall from the appropriate authority to a watercourse, creek, river or the sea for drainage discharge.^{[26] (page38 to 40)}

Road construction on Marquette Avenue in Minneapolis, Minnesota, United States

A borrow pit (source for obtaining fill, gravel, and rock) and a water source should be located near or in reasonable distance to the road construction site. Approval from local authorities may be required to draw water or for working (crushing and screening) of materials for construction needs. The top soil and vegetation is removed from the borrow pit and stockpiled for subsequent rehabilitation of the extraction area. Side slopes in the excavation area not steeper than one vertical to two horizontal for safety reasons.^{[26] (page 53 to 56 )}

Old road surfaces, fences, and buildings may need to be removed before construction can begin. Trees in the road construction area may be marked for retention. These protected trees should not have the topsoil within the area of the tree's drip line removed and the area should be kept clear of construction material and equipment. Compensation or replacement may be required if a protected tree is damaged. Much of the vegetation may be mulched and put aside for use during reinstatement. The topsoil is usually stripped and stockpiled nearby for rehabilitation of newly constructed embankments along the road. Stumps and roots are removed and holes filled as required before the earthwork begins. Final rehabilitation after road construction is completed will include seeding, planting, watering and other activities to reinstate the area to be consistent with the untouched surrounding areas.^{[26] (page 66 to 67 )}

Processes during earthwork include excavation, removal of material to spoil, filling, compacting, construction and trimming. If rock or other unsuitable material is discovered it is removed, moisture content is managed and replaced with standard fill compacted to 90% relative compaction. Generally blasting of rock is discouraged in the road bed. When a depression must be filled to come up to the road grade the native bed is compacted after the topsoil has been removed. The fill is made by the "compacted layer method" where a layer of fill is spread then compacted to specifications, the process is repeated until the desired grade is reached.^{[26] (page 68 to 69 )}.

Line marking

General fill material should be free of organics, meet minimum California bearing ratio (CBR) results and have a low plasticity index. The lower fill generally comprises sand or a sand-rich mixture with fine gravel, which acts as an inhibitor to the growth of plants or other vegetable matter. The compacted fill also serves as lower-stratum drainage. Select second fill (sieved) should be composed of gravel, decomposed rock or broken rock below a specified Particle size and be free of large lumps of clay. Sand clay fill may also be used. The road bed must be "proof rolled" after each layer of fill is compacted. If a roller passes over an area without creating visible deformation or spring the section is deemed to comply.^{[26] (page 70 to 72 )}

Geosynthetics such as geotextiles, geogrids and geocells are frequently used in the various pavement layers to improve road quality. Geosynthetics perform four main functions in roads: separation, reinforcement, filtration and drainage; which increase the pavement performance, reduce construction costs and decrease maintenance.^[29]

The completed road way is finished by paving or left with a gravel or other natural surface. The type of road surface is dependent on economic factors and expected usage. Safety improvements like Traffic signs, Crash barriers, Raised pavement markers, and other forms of Road surface marking are installed.

According to a May 2009 report by the American Association of State Highway and Transportation Officials (AASHTO) and TRIP—a national transportation research organization—driving on rough roads costs the average American motorist approximately $400 a year in extra vehicle operating costs. Drivers living in urban areas with populations more than 250,000 are paying upwards of $750 more annually because of accelerated vehicle deterioration, increased maintenance, additional fuel consumption, and tire wear caused by poor road conditions.

When a single carriageway road is converted into dual carriageway by building a second separate carriageway alongside the first, it is usually referred to as duplication,^[30] twinning or doubling. The original carriageway is changed from two-way to become one-way, while the new carriageway is one-way in the opposite direction. In the same way as converting railway lines from single track to double track, the new carriageway is not always constructed directly alongside the existing carriageway.

Maintenance[link]

"Road works ahead" sign, typically used in Europe

Like all structures, roads deteriorate over time. Deterioration is primarily due to accumulated damage from vehicles, however environmental effects such as frost heaves, thermal cracking and oxidation often contribute.^[31] According to a series of experiments carried out in the late 1950s, called the AASHO Road Test, it was empirically determined that the effective damage done to the road is roughly proportional to the Fourth power of axle weight.^[32] A typical tractor-trailer weighing 80,000 pounds (36.287 t) with 8,000 pounds (3.629 t) on the steer axle and 36,000 pounds (16.329 t) on both of the tandem axle groups is expected to do 7,800 times more damage than a passenger vehicle with 2,000 pounds (0.907 t) on each axle. Potholes on roads are caused by rain damage and vehicle braking or related construction works.

Manual road repair taking place in Howrah, India.

Pavements are designed for an expected service life or design life. In some UK countries the standard design life is 40 years for new bitumen and concrete pavement. Maintenance is considered in the whole life cost of the road with service at 10, 20 and 30 year milestones.^[33] Roads can be and are designed for a variety of lives (8-, 15-, 30-, and 60-year designs). When pavement lasts longer than its intended life, it may have been overbuilt, and the original costs may have been too high. When a pavement fails before its intended design life, the owner may have excessive repair and rehabilitation costs. Many concrete pavements built since the 1950s have significantly outlived their intended design lives.^[34] Some roads like Chicago, Illinois's "Wacker Drive", a major two-level viaduct in downtown area are being rebuilt with a designed service life of 100 years.^[35]

Virtually all roads require some form of maintenance before they come to the end of their service life. Pro-active agencies use pavement management techniques to continually monitor road conditions and schedule preventive maintenance treatments as needed to prolong the lifespan of their roads. Technically advanced agencies monitor the road network surface condition with sophisticated equipment such as laser/inertial Profilometers. These measurements include road curvature, cross slope, asperity, roughness, rutting and texture (roads). This data is fed into a pavement management system, which recommends the best maintenance or construction treatment to correct the damage that has occurred.

Maintenance treatments for asphalt concrete generally include crack sealing, surface rejuvenating, fog sealing, micro-milling and surface treatments. Thin surfacing preserves, protects and improves the functional condition of the road while reducing the need for routing maintenance, leading to extended service life without increasing structural capacity.^[36]

Failure to maintain roads properly can create significant costs to society, in a 2009 report released by the American Association of State Highway and Transportation Officials (USA) about 50% of the roads in the USA are in bad condition with urban areas worse. The report estimates that urban drivers pay an average of $746/year on vehicle repairs while the average US motorist pays about $335/year. In contrast, the average motorist pays about $171/year in road maintenance taxes (based on 600 gallons/year and $0.285/gallon tax).

Slab Stabilization[link]

Distress and serviceability loss on concrete roads can be caused by loss of support due to voids beneath the concrete pavement slabs. The voids usually occur near cracks or joints due to surface water infiltration. The most common causes of voids are pumping, consolidation, subgrade failure and bridge approach failure. Slab stabilization is a non-destructive method of solving this problem and is usually employed with other Concrete Pavement Restoration (CPR) methods including patching and diamond grinding. The technique restores support to concrete slabs by filing small voids that develop underneath the concrete slab at joints, cracks or the pavement edge. The process consists of pumping a cementitous grout or polyurethane mixture through holes drilled through the slab. The grout can fill small voids beneath the slab and/or sub-base. The grout also displaces free water and helps keep water from saturating and weakening support under the joints and slab edge after stabilization is complete. The three steps for this method after finding the voids are locating and drilling holes, grout injection and post-testing the stabilized slabs.

Slab stabilization does not correct depressions, increase the design structural capacity, stop erosion or eliminate faulting. It does, however, restore the slab support, therefore, decreasing deflections under the load. Stabilization should only be performed at joints and cracks where loss of support exists. Visual inspection is the simplest manner to find voids. Signs that repair is needed are transverse joint faulting, corner breaks and shoulder drop off and lines at or near joints and cracks. Deflection testing is another common procedure utilized to locate voids. It is recommended to do this testing at night as during cooler temperatures, joints open, aggregate interlock diminishes and load deflections are at their highest.

Testing[link]

Ground penetrating radar pulses electromagnetic waves into the pavement and measures and graphically displays the reflected signal. This can reveal voids and other defects.

The epoxy/core test, detects voids by visual and mechanical methods. It consists of drilling a 25 to 50 millimeter hole through the pavement into the sub-base with a dry-bit roto-hammer. Next, a two-part epoxy is poured into the hole—dyed for visual clarity. Once the epoxy hardens, technicians drill through the hole. If a void is present, the epoxy will stick to the core and provide physical evidence.

Common stabilization materials include pozzolan-cement grout and polyurethane. The requirements for slab stabilization are strength and the ability to flow into or expand to fill small voids. Colloidal mixing equipment is necessary to use the pozzolan-cement grouts. The contractor must place the grout using a positive-displacement injection pump or a non-pulsing progressive cavity pump. A drill is also necessary but it must produce a clean hole with no surface spalling or breakouts. The injection devices must include a grout packer capable of sealing the hole. The injection device must also have a return hose or a fast-control reverse switch, in case workers detect slab movement on the uplift gauge. The uplift beam helps to monitor the slab deflection and has to have sensitive dial gauges.^[37][38]

Joint Sealing[link]

Also called joint and crack repair, this method’s purpose is to minimize infiltration of surface water and incompressible material into the joint system. Joint sealants are also used to reduce dowel bar corrosion in Concrete Pavement Restoration (CPR) techniques. Successful resealing consists of old sealant removal, shaping and cleaning the reservoir, installing the backer rod and installing the sealant. Sawing, manual removal, plowing and cutting are methods used to remove the old sealant. Saws are used to shape the reservoir. When cleaning the reservoir, no dust, dirt or traces of old sealant should remain. Thus, it is recommended to water wash, sand-blast and then air blow to remove any sand, dirt or dust. The backer rod installation requires a double-wheeled, steel roller to insert the rod to the desired depth. After inserting the backer rod, the sealant is placed into the joint. There are various materials to choose for this method including hot pour bituminous liquid, silicone and preformed compression seals.

^{[37][39][40][41]}

Safety considerations[link]

Pedestrian crossing, line markings and street furniture.

Careful design and construction of roads can increase Road traffic safety and reduce the harm (deaths, injuries, and property damage) on the highway system from traffic collisions.

On neighborhood roads traffic calming, safety barriers, pedestrian crossings and cycle lanes can all protect pedestrians and cyclists.

Lane markers in some countries and states are marked with Cat's eyes or Botts dots, bright reflectors that do not fade like paint. Botts dots are not used where it is icy in the winter, because frost and snowplows can break the glue that holds them to the road, although they can be embedded in short, shallow trenches carved in the roadway, as is done in the mountainous regions of California.

For major roads risk can be reduced by providing limited access from properties and local roads, grade separated junctions and median dividers between opposite-direction traffic to reduce likelihood of head-on collisions.

The placement of energy attenuation devices (e.g. guardrails, wide grassy areas, sand barrels) is also common. Some road fixtures such as road signs and fire hydrants are designed to collapse on impact. Light poles are designed to break at the base rather than violently stop a car that hits them. Highway authorities may also remove larger trees from the immediate vicinity of the road.

Environmental performance[link]

Air pollution along Pasadena Highway in Los Angeles, United States

Careful design and construction of a road can reduce any negative environmental impacts.

Water management systems can be used to reduce the effect of pollutants from roads.^{[citation needed]} Rainwater and snowmelt running off of roads tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants and result in Water pollution. Road runoff is a major source of nickel, copper, zinc, cadmium, lead and polycyclic aromatic hydrocarbons (PAHs), which are created as combustion byproducts of gasoline and other fossil fuels.^[42] De-icing chemicals and sand can run off into roadsides, contaminate groundwater and pollute surface waters;^[43] and road salts can be toxic to sensitive plants and animals.^[44] Sand applied to icy roads can be ground up by traffic into fine particulates and contribute to air pollution. Sand can alter stream bed environments, causing stress for the plants and animals that live there.^{[citation needed]}

Roads are a chief source of environmental noise generation. In the early 1970s it was recognized that design of roads can be conducted to influence and minimize noise generation.^[45] Noise barriers are used to reduce Noise pollution, in particular where roads are located close to built-up areas. Regulations can restrict the use of Engine braking.

Motor vehicle emissions contribute air pollution. Concentrations of air pollutants and adverse respiratory health effects are greater near the road than at some distance away from the road.^[46] Road dust kicked up by vehicles may trigger allergic reactions.^[47]

Terminology[link]

The A22(T) with line markings near Summer Hill, East Sussex, England, United Kingdom

Road with guard rails in Kaluga Oblast, Russia

Road with traffic signs in the outskirts of Bern, Switzerland

Highway 401, a route with a collector / express setup.

The wide Coastal Road in the Philippines now called the Manila Cavite Expressway

Road in the Jujuy Province Argentina

• Alignment - the route of the road, defined as a series of horizontal tangents and curves.
• Adverse camber - where a road slopes towards the outside of a bend, increasing the likelihood that vehicles travelling at speed will skid or topple. Usually only a temporary situation during road maintenance.
• All-weather road - Unpaved road that is constructed of a material that does not create mud during rainfall.
• Banked turn
• Camber or Crown - the slope of the road surface downwards away from the centre of the road, so that surface water can flow freely to the edge of the carriageway, or on bends angling of the surface to lean traffic 'into the bend' reducing the chance of a skid.
• Cant - superelevation
• Cross slope The slope of the pavement, expressed as units of rise per unit of run, or as a percentage.
• Grade - longitudinal slope
• Belisha Beacon - an orange globe, lit at night, used to highlight a pedestrian crossing.
• Bollard - Rigid posts that can be arranged in a line to close a road or path to vehicles above a certain width
• Byway - Highway over which the public have a right to travel for vehicular and other kinds of traffic, but is used mainly as a footpath or bridleway
• Bypass Road that avoids or "bypasses" a built-up area, town, or village
• Bottleneck - Section of a road with a carrying capacity substantially below that of other sections of the same road
• Botts' dots - Non-reflective raised pavement marker used on roads
• Cat's eye - reflective raised pavement marker used on roads
• Central reservation - On dual carriageway roads, including controlled-access highways, divided highways and many limited-access roads, the central reservation (British English), median (North American English), median strip (North American English and Australian English), neutral ground [Louisiana English] or central nature strip (Australian English) - Area that separates opposing lanes of traffic
• Chicane - Sequence of tight serpentine curves (usually an S-shape curve or a bus stop)
• Chipseal - Road surface composed of a thin layer of crushed stone 'chips' and asphalt emulsion. It seals the surface and protects it from weather, but provides no structural strength. It is cheaper than asphalt concrete or concrete. In the U.S. it is usually only used on low volume rural roads
• Corniche - Road on the side of a cliff or mountain, with the ground rising on one side and falling away on the other
• Curb (kerb) - A raised edge at the side of the roadway.
• Curb extension - (also kerb extension, bulb-out, nib, elephant ear, curb bulge and blister) Traffic calming measure, intended to slow the speed of traffic and increase driver awareness, particularly in built-up and residential neighborhoods.
• Drainage gradient
• Farm-to-market road - a state road or county road that connects rural or agricultural areas to market towns.
• Fork - (literally "fork in the road") Type of intersection where a road splits
• Green lane - (UK) Unsurfaced road, may be so infrequently used that vegetation colonises freely, hence 'green'. Many green lanes are ancient routes that have existed for millennia.
• Guide rail - Prevents vehicles from veering off the road into oncoming traffic, crashing against solid objects or falling from a road. Also called a guard rail or traffic barrier.
• Gutter (UK) - a drainage channel usually at the edge of the road or along a median.
• Interstate Highway System (United States) - System of Interstate and Defense Highways
• Layby (Pullout, pull-off) - A paved area beside a main road where cars can stop temporarily to let another car pass.
• Loose chippings - the hazard of stone chippings that have come loose
• Median - On dual carriageway roads, including controlled-access highways, divided highways and many limited-access roads, the central reservation (British English), median (North American English), median strip (North American English and Australian English), neutral ground [Louisiana English] or central nature strip (Australian English) - Area that separates opposing lanes of traffic
• Mountain pass - A relatively low level route through a range of mountains
• Milestone - One of a series of numbered markers placed along a road, often at regular intervals, showing the distance to destinations.
• National Highway - Road built and maintained by a national authority.
• Pavement - The road regarded as a geoconstruction. In the UK the term is road surface and the pavement is a pedestrian walkway alongside the road.
• Pedestrian crossing - Designated point on a road where road marking or other means helps pedestrians cross safely
• Pelican crossing - (officially Pelicon crossing) UK a PEdestrian LIght CONtrolled crossing.
• Private highway - Highway owned and operated for profit by private industry
• Private road - Road owned and maintained by a private individual, organization, or company rather than by a government
• Profile - the vertical alignment of a road, expressed as a series of grades, connected by parabolic curves.
• Public space - Place where anyone has a right to come without being excluded because of economic or social conditions
• Ranch road - U.S. road that connects rural and agricultural areas to market towns
• Road number - Often assigned to identify a stretch of public roads— often dependent on the type of road, with numbers differentiating between interstates, motorways, arterial thoroughfares, etc.
• Road-traffic safety - Process to reduce the harm (deaths, injuries, and property damage) that result from vehicle crashes on public roads
• Roadworks - Part or all of the road is occupied for work or maintenance
• Roughness - Deviations from a true planar pavement surface, which affects vehicle suspension deflection, dynamic loading, ride quality, surface drainage and winter operations. Roughness have wavelengths ranging from 500 mm up to some 40 m. The upper limit may be as high as 350 m when considering motion sickness aspects; motion sickness is generated by motion with down to 0.1 Hz frequency; in an ambulance car driving 35 m/s (126 km/h), waves with up to 350 m will excite motion sickness.
• Roundabout UK a road junction where typically three or more roads are joined by a circular section of road. Traffic 'on the roundabout' has priority over traffic on approach roads, unless indicated otherwise. In countrys where traffic drives on the left the roundabout is travelled in a clockwise direction. Also known as an island in parts of the UK.
• Shoulder (also hard shoulder) - A clear, level area to the side of the roadway available for stopping if needed.
• State highway - Road numbered by the state, falling below numbered national highways (like U.S. Routes) in the hierarchy or a road maintained by the state, including nationally-numbered highways
• Traffic - Pedestrians, ridden or herded animals, vehicles, bicycles, and other conveyances using any road for purposes of travel. ^[48].
• Texture (roads) - Deviations from a true planar pavement surface, which affects the interaction between road and tire. Microtexture have wavelengths below 0.5 mm, Macrotexture below 50 mm and Megatexture below 500 mm.
• Traffic calming - Set of strategies used by urban planners and traffic engineers to slow down or reduce motor vehicle traffic, thereby improving safety for pedestrians and bicyclists and improving the environment for residents
• Traffic island - UK a small raised area used to help define the traffic flow, which may also act as a refuge for pedestrians crossing the carriageway or a location for signs, barriers or lights—a synonym for roundabout in some parts of the UK
• Traffic light - Also known as a traffic signal, stop light, stop-and-go lights—a signaling device at a road intersection, pedestrian crossing, or other location that assigns right of way to different approaches to an intersection
• Zebra crossing (UK) - a pedestrian crossing marked by black and white stripes on the carriageway

Regulation[link]

Right- and left-hand traffic[link]

Traffic flows on the right or on the left side of the road depending on the country.^[49] In countries where traffic flows on the right, traffic signs are mostly on the right side of the road, roundabouts and traffic circles go counter-clockwise/anti-clockwise, and pedestrians crossing a two-way road should watch out for traffic from the left first.^[50] In countries where traffic flows on the left, the reverse is true.

About 33% of the world by population drive on the left, and 67% keep right. By road distances, about 28% drive on the left, and 72% on the right,^[51] even though originally most traffic drove on the left worldwide.^[52]

Economics[link]

A city street in Mumbai, India with left-hand traffic.

Transport economics is used to understand both the relationship between the transport system and the wider economy and the complex network effects when there are multiple paths and competing modes for both personal and freight (road/rail/air/ferry) and where Induced demand can result in increased on decreased transport levels when road provision is increased by building new roads or decreased (for example California State Route 480). Roads are generally built and maintained by the public sector using taxation although implementation may be through private contractors).^[53][54] or occasionally using road tolls.^[55]

Public-private partnerships are a way for our communities to address the rising cost by injecting private funds into our infrastructure. There are four main ones:^[56]

• design/build
• design/build/operate/maintain
• design/build/finance/operate
• build/own/operate

Economics and society depend heavily on efficient roads. In the European Union (EU) 44% of all goods are moved by trucks over roads and 85% of all persons are transported by cars, buses or coaches on roads.^[57] The term was also commonly used to refer to roadsteads, waterways that lent themselves to use by shipping.

Construction costs[link]

According to the New York State Thruway Authority,^[58] some sample per-mile costs to construct multi-lane roads in several US northeastern states were:

• Connecticut Turnpike — $3,449,000 per mile
• New Jersey Turnpike — $2,200,000 per mile
• Pennsylvania Turnpike (Delaware Extension) — $1,970,000 per mile
• Northern Indiana Toll Road — $1,790,000 per mile
• Garden State Parkway — $1,720,000 per mile
• Massachusetts Turnpike — $1,600,000 per mile
• Thruway, New York to Pennsylvania Line — $1,547,000 per mile
• Ohio Turnpike — $1,352,000 per mile
• Pennsylvania Turnpike (early construction) — $736,000 per mile

Statistics[link]

The United States has the largest network of roads of any country with 4,050,717 miles (6,518,997 km) as of 2009.^[59] The People's Republic of China is second with 3,583,715 kilometres (2,226,817 mi) of road (2007) See List of countries by road network size. The Republic of India has the third largest road system in the world with 3,383,344 kilometres (2,102,312 mi) (2002). When looking only at expressways the National Trunk Highway System (NTHS) in People's Republic of China has a total length of 45,000 kilometres (28,000 mi) at the end of 2006, and 60,300 km at the end of 2008, second only to the United States with 90,000 kilometres (56,000 mi) in 2005.^[60][61]

Many human settlements are not reachable by road alone. Road vehicles must be carried by boat or ferry to islands, and some locations are intentionally car-free. Even on the mainland, some settlements have no roads connecting with the main continental network, due to natural obstacles like mountains or wetlands, remoteness, or general expense. Unpaved roads or lack of roads are more common in developing countries, though even large cities like Iquitos in Peru and Juneau, Alaska in the United States are disconnected.

See also[link]

References[link]

Lisa Kelly
Birth name	Laoise Ní Cheallaigh
Born	(1977-05-07) 7 May 1977 (age 35) Dublin, Ireland
Genres	Celtic, Classical
Occupations	Singer
Instruments	Vocals, Piano
Labels	Celtic Collections Manhattan
Associated acts	Celtic Woman
Website	lisakellysite.com

Lisa Ann Kelly (Irish Laoise Ní Cheallaigh, born 7 May 1977) is a singer of both classical and celtic music. She has taken part in many musical theatre productions and concerts, and is a member of the musical group Celtic Woman.

Early life[link]

Lisa Kelly was born in Dublin, into a musical family, with both her parents and sisters being singers. Lisa herself has been singing since the age of seven, when she starred in the musical version of Bugsy Malone. Her parents are both heavily involved in amateur theatre, influencing Lisa toward studying drama, as well as being classically trained in both piano and singing.

Music career[link]

She has played several principal roles, such as "Velma Kelly" in Chicago, "Florence" in Chess, "Laurey" in Oklahoma!, "Maria" in West Side Story and "Sandy" in Grease.

She has also performed in a number of concerts in Dublin's National Concert Hall, including The Magic of Gershwin, The Music of Cole Porter and From Romberg to Rodgers, and has won numerous national awards for singing and drama.

Riverdance[link]

After deciding to take a break from her day job in the computer industry to return to theatre, she played the lead role in the Christmas pantomime Jack and the Beanstalk at Dublin's Gaiety Theatre. This led to her being cast in the American production of Riverdance – The Show as lead female vocalist in 2000, a position she held for five years while touring. While touring with Riverdance, Lisa met Australian dancer Scott Porter, who later became her husband.

Solo album[link]

In 2002, Lisa was asked to record a solo album with director David Downes on the Celtic Collections label. The resulting debut album, Lisa, was released in 2003. Songs featured on this CD are "Carrickfergus", "Siúil A Rún", "The Deer's Cry", "Lift the Wings", "The Soft Goodbye", "Home and the Heartland", "Homecoming", "Now We Are Free", "Dubhdarra", "May It Be", and "Send Me a Song".

Celtic Woman[link]

Lisa was again approached by Downes in 2004, and asked to be part of Celtic Woman, originally planned as a one-night event at Dublin's Helix Theatre. The group has since released several albums and DVD performances of their concerts and embarked on several world tours.

She says she accepted a spot in Celtic Woman because "I wasn't doing anything else that day." She did not know any of the artists she would be performing with when they first got together but Kelly stated that "the show is blessed with the girls [the show's creators] picked."^[1] She has toured with Celtic Woman throughout most of their tours and appears in every CD and DVD to date.

Lisa performs several songs with Celtic Woman. She sings "Send Me a Song" and "The Blessing", both originals that have been featured on the original and A New Journey CDs, DVDs, and tours respectively. They were written by David Downes and feature him on the piano. Another song written by David Downes is "Green the Whole Year Round", which has been featured on the Christmas Celebration DVD and Greatest Journey CD and DVD, but not any tour. Lisa performs "The Voice" in A New Journey, which was originally supposed to be sung by Méav Ní Mhaolchatha, and also features fiddler Máiréad Nesbitt. "The Voice" was written by Irish novelist and composer Brendan Graham. Another song that Lisa performs in the original performance is "May It Be", originally from the movie The Lord of the Rings: The Fellowship of the Ring. Lisa sings "Caledonia" in A New Journey, and sang Sting's "Fields of Gold" during the Isle of Hope and Songs From the Heart tours. In Songs From the Heart, she also sings "The Moon's a Harsh Mistress," accompanied by Máiréad Nesbitt on the violin.

During the A New Journey tour, and again during the "Believe" tour, Lisa took a break for the birth of her children. She was replaced by Alex Sharpe who later became a full-time member of Celtic Woman when Orla Fallon left. Later she was replaced by Susan Mcfadden. ^[2]

Other[link]

In 2009, Lisa Kelly sang the main title song If You Believe for the Disney movie Tinkerbell – The Lost Treasure.^[3]

In December 2011 Lisa Kelly announced she was taking a maternity leave and will not be in the 2012 Believe Tour. She is being replaced by Susan McFadden.

Personal life[link]

Lisa is married to Australian dancer Scott Porter. They have three children: sons Cian and Jack and daughter Ellie. She calls them, "hands down, the most important parts of my life", and they accompany her on tour when they are not in school. Lisa's sister Helen has performed with Celtic Woman in the choir. As of December 2011^[update] Lisa is pregnant with their fourth child.

Discography[link]

• Lisa (2003; re-release 2006)
• Celtic Woman (March 2005)
• Celtic Woman: A Christmas Celebration (October 2006)
• Celtic Woman: A New Journey (January 2007)
• Celtic Woman: The Greatest Journey (October 2008)
• Celtic Woman: Songs from the Heart (January 2010)
• Celtic Woman: Lullaby (February 2011)
• Celtic Woman: Believe (May 2011; January 2012)

References[link]

External links[link]

• Lisakellysite.com – Official website
• Lisa Kelly at the Internet Movie Database