Road salt is a clear, brittle mineral used to melt ice and snow or to prevent their build-up in cold weather. Road salt can be poured from bags or spread on roads by a specially equipped truck. It is also called rock salt. Road salt consists of sodium chloride, the same chemical that makes up table salt . But road salt is coarser. It is usually dark gray in color. Adding salt to water lowers the water’s freezing point , which can prevent it from turning into ice. However, salt is not very effective when temperatures drop below around 15 °F (-9 °C). Workers may add other minerals—such as magnesium chloride or calcium chloride—to road salt to help it work at temperatures below this range.
Road salt is mined from large deposits of salt left behind when prehistoric oceans evaporated. The largest deposits in the United States are mined in Kansas, Louisiana, Michigan, Ohio, and New York. Road crews in the United States use about 20 million tons (18 million metric tons) of salt each winter. Salting roadways can greatly reduce motor vehicle accidents during and after a snowstorm.
The use of road salt also has harmful consequences. Salt corrodes (wears away at) such infrastructure as bridges and roads. It can also cause automobiles to rust . Excess salt is often washed into rivers and lakes or seeps into groundwater used for drinking. Environmental researchers estimate that almost 70 percent of road salt enters the water system. Excessive salt can harm or kill fish and water plants. Exposure to excess salt may harm roadside trees, causing their leaves to turn brown or killing their branches. Road crews have experimented with alternatives to road salt, such as beet juice or pickle brine. But these substances can cause their own environmental problems—for example, adding sugar to the ecosystem, which can contribute to the spread of harmful microorganisms.
Before World War II (1939-1945), local governments cleared roadways by plowing them and spreading sand for traction. Some people put snow chains on their car tires. In 1938, New Hampshire became the first state to widely use road salt. By the winter of 1941-1942, salting roadways was a common practice throughout the state. Road salt came into regular use across the United States and Canada in the 1950’s. People first became aware of the damaging environmental effects of road salt use in the 1970’s.
