According to the website Vox.com before World War II, few US cities used salt in the winter. When snow fell, local governments would plow the roads and then spread sand and cinders around to improve traction. Cars would don snow chains, and people generally accepted that the roads weren't always passable in icy conditions. But as America's highways expanded and became ever more crucial to the economy, that changed. Increasingly, truckers and commuters needed to be able to drive in all conditions. New Hampshire's state government became the first to use salt on the roads in the winter of 1941–'42, and the practice spread as the interstate highway system was built in the 195-‘s and grew. Road salt is basically sodium chloride — much like table salt — and comes from deposits leftover after prehistoric oceans evaporated, with huge mines in Ohio, Michigan, New York, Kansas, and Louisiana. Oftentimes, extra chemicals will be mixed in. For instance, road salt is less effective at melting ice when temperatures drop below 20 degrees — when it gets extremely cold, other chemicals like magnesium chloride or calcium chloride are mixed in. Salt, after all, has plenty of drawbacks. It can corrode the steel in cars, trucks, bridges, and reinforcing rods in concrete — weakening valuable infrastructure. Transportation departments can add chemicals to the salt to inhibit corrosion or add coating to steel, but this gets pricey. One study in Utah estimated that salt corrosion now costs the US almost $20 billion a year. Salt dissolves and splits into sodium and chloride, it washes away, into rivers and streams. Chloride, in particular, doesn't get filtered out naturally by soil and accumulates in waterways. In December 2014, the US Geological Survey found that chloride levels were on the rise in 84 percent of urban streams studied — with 29 percent exceeding federal safety limits. On December 10, 1699 in one of the first major ice storms in New England recorded history, ice shut down the city of Boston for a week – there was no salt or anything else to cause the ice to melt as temperatures remain very cold for days. In addition, the ice caused massive damage to orchards in the region as the heavy frozen rain brought down many tree limbs.
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