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Ice roads or ice bridges are frozen structures formed over bays, inlets, rivers or lake surfaces. An ice bridge is a structure which is typically formed during glaciation, and may be related to a significant migration of prehistoric peoples. Ice roads are simply seasonal occurrences that facilitate transportation to and from areas without permanent roads, and are commonly seen in isolated regions in Canada's north and Alaska's bush.

Contents 1 Ice bridge 2 Ice road 3 Ice roads around the world 3.1 Estonia 3.2 Finland 4 See also 5 References 6 External links

An ice bridge is a frozen natural structure formed over seas, bays, rivers or lake surfaces. They facilitate migration of animals or people over a water body that was previously uncrossable by terrestrial animals, including humans. The most significant ice bridges are formed by glaciation, spanning distances of many miles over sometimes relatively deep water bodies. An example of such a major ice bridge was that connecting the island of Öland with mainland Sweden approximately 9000 BC. This bridge reached its maximum utility when the glacier was in retreat forming a low lying frozen bridge. The Öland ice bridge allowed the first human migration to the island of Öland, which is most readily documented by archaeological studies of the Alby People.^[1]

Sometimes ice bridges are merely seasonal formations, providing transportation to and from communities without permanent roads, and are commonly seen in isolated regions in Canada's north. They may also be seasonal surrogates for the summer ferry service. In general, these bridges are used in areas where construction of year-round roads is expensive. When frozen in winter, the river can be built up with a system of auger holes to flood and thicken the crossing. Depending on the region, these seasonal ice bridges last anywhere from a few weeks to several months before they become impassable.

Ice roads play a crucial role in the transportation of goods to communities without permanent road access. In many of these communities, air transportation is used at other times of the year to bring in goods including food and supplies, but this can be prohibitively costly for bulky goods such as building supplies and heavy equipment.

In general, these roads occur (often with human assistance) in areas where construction of year-round roads is expensive due to the presence of boggy muskeg land. When frozen in winter, these obstacles are easier to cross. In the case of ice roads such as the stretch from Inuvik and Tuktoyuktuk, Northwest Territories, Canada provides an almost level driving surface with few detours several months of the year.

Where possible, ice roads may be intentionally built across frozen lakes, which ironically provide the best surface for driving on in winter. Completely flat, and devoid of trees, rocks and other obstacles, the lakes are easier to clear a path across than bare land. The roads built from Yellowknife to Port Radium by John Denison, an early pioneer of ice roads in the Canadian Arctic 1950s-1970s, were almost entirely plowed across frozen lakes, with a short overland portage between the shoreline of one lake and the beginning of the next.

After an ice road is plowed across a lake, the ice there gets much thicker than the surrounding lake ice, because the snow cover has been swept off—exposing the road directly to subfreezing air with temperatures as low as -60 °F (-51 °C). 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.

While easier to drive across in the winter than land, frozen lakes still present a great danger to truckers hauling cargo across. Speeds are generally limited to 15 miles per hour (25 km/h) to prevent the weight of a truck from starting waves under the lake surface, which can 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 over time due to heat.

Depending on the region, ice roads last anywhere from a few weeks to several months before they become impassable. The roads are normally the domain of large trucks, although cars are occasionally seen.

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 inches) along the entire route. Ice roads are mostly used between mainland Estonia and islands off the west coast. The limitations for ice road traffic include:

• Weight limit depending on conditions, mostly 2-2.5 tonnes
• Minimal distance between vehicles travelling in the same direction must be at least 250 m
• Recommended travelling speeds are under 25 km/h (16 mph) or between 40-70 km/h (25-45 mph). It is advised to avoid the range of 25-40 km/h due to danger of creating resonance in the ice layer.
• Seat belts must not be fastened due to danger of drowning in case of ice breakage
• The vehicle must not be stopped
• Vehicles are allowed to enter the ice road in 3-minute intervals
• Ice roads may only be used in daylight

Finnish Road Administration maintains some ice roads during winters. These roads are considered as public roads when they are open. Ice must be at least 40 cm (16 in) thick before the road may be opened.

Following limits apply to ice roads:

• Weight limit 3 tonnes (may be raised if ice is thick enough)
• Speed limit 50 km/h (30 mph)
• Minimum space of 50 m (160 ft) between cars traveling in the same direction.

• Ice Road Truckers - History Channel series
• Road of Life - Ice road across the frozen Lake Ladoga in Russia, which provided the only access to the besieged city of Leningrad in the winter months during World War II
• Tibbitt to Contwoyto Winter Road
• Winter road
• List of Northwest Territories highways
• Highways in Nunavut

• Government of NWT-Ice Roads/Bridges
• Government of NWT Highway Condition Reports
• Building Canada's Epic Ice Road, Popular Mechanics article.

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