It's everywhere these days - spread like chicken feed on steps, showered on parking lots and dumped on roads by the ton.
But the science of salt has changed over the years, with highway crews applying more anti-icing agent - a liquid salt brine - just before each snowfall. Crews also no longer wait for snow to accumulate before spreading salt.
"As soon as there's enough snow on the road to hold down any of that salt, we're putting it down," said Mark Lipnick, a State Highway Administration quality assurance engineer.
He said that state highway crews used to wait until about an inch of snow was on roads before spreading salt.
But research and experience showed that a key to keeping roads clear is preventing a bond from forming between the road and the snow that falls on it. The molecular bond becomes more and more likely to form as temperatures drop.
The salt that crews spread on Maryland highways is made up of two elements, sodium and chloride. The compound is a byproduct of oceans that dried up and formed continents millions of years ago. It melts snow by depressing water's freezing point.
It is one of the most abundant compounds on earth, it has been spread on highways since the 1930s and its use is a result of cost and climate.
Most snow in the United States falls when temperatures are between 25 and 32 degrees Fahrenheit, which makes salt ideal, according to the Salt Institute, an industry trade group based in Washington.
It also is relatively cheap: Maryland - which must clear 16,000 miles of state highways with each storm - pays about $30 a ton. In recent winters, the tab for salt has come to about $30 million a year, state officials say - a figure that does not include the costs for local governments.
Nationally, governments, businesses and homeowners paid $336 million for 13 million tons of salt last year, according to the institute.
But the price may be worth it - particularly if you're a politician.
Michael A. Bilandic was defeated in his bid to be re-elected as mayor of Chicago in 1979 shortly after he failed to sufficiently salt streets during a terrible blizzard. Shortages of salt for Baltimore County's roads in early 1994 forced the county to use slag and contributed to the defeat of County Executive Roger B. Hayden that year.
