- The Washington Times - Wednesday, February 18, 2004

Snowy forecasts bring joy to schoolchildren and goose bumps to skiers. To those charged with keeping the nation’s roadways clear, the blustery news means it’s time to apply a little scientific know-how.

It takes more than just dumping tons of rock salt onto the highways and byways to keep the roads clear of snow and slush. Road crews must consider a quiver full of chemical alternatives to keep innocent snow from forming into dangerous sheets of ice. They also must judge exactly when to deploy their salt-based weapons.

Bill Mahoney, program manager of the National Center for Atmospheric Research in Boulder, Colo., says modern departments of transportation piggyback their snow-fighting efforts onto the latest weather forecasting models.

State and local departments of transportation look at the predicted road conditions based on weather forecasts and provide treatment recommendations on a route-by-route basis, Mr. Mahoney says.

It wasn’t always that way.

“In the old days, about five years ago, most of the departments of transportation worried only about putting sand down and salt. That was pretty much the options,” he says. “Now we focus on environmental stewardships and overtime costs. … They have to be a lot smarter with dealing with the roadways.”

Walter Witschey, director of the Science Museum of Virginia in Richmond, says the salt used on the nation’s roadways isn’t much different from what’s shaken on french fries in the average burger joint.

“The salt used by the road people is mined and crushed to the right granular size and used directly,” Mr. Witschey says. “It hasn’t been refined or purified, but chemically it’s salt.”

What that salt, sodium chloride by its chemical name, does is affect the “freezing-point depression,” Mr. Witschey says. That’s the fancy term for lowering the point at which water becomes ice from the standard 32 degrees Fahrenheit. Salt compounds can shrink that number by 10 degrees to 15 degrees.

Salt, when combined with water, creates a brine solution in which the sodium ions separate from the chlorine ions. Both sets of ions work to reduce the freezing mark.

“There are a lot of other chemicals which will do this,” Mr. Witschey says, including calcium chloride and magnesium chloride.

Sodium chloride often gets the call because it costs less than other alternatives.

Treating roads, Mr. Mahoney says, has become “quite an art form.”

“Sometimes, they put the chemicals down wet, sometimes dry,” he says. Workers have to analyze traffic levels, drifting snow, rush hours and other factors before making a decision.

Often, all the factors hinge on just how cold the roadways are at the start of the storm.

“It all depends on the road temperatures,” Mr. Mahoney says. “When the pavement temperature is between 15 degrees and freezing, they can actually use salt. Below 15 degrees, they have to use calcium chloride or, if it’s really cold, abrasives.”

Those abrasives range from simple sand to ash, giving car tires a fighting chance to grab the slick roads.

Some states spray a solution of magnesium chloride a few hours before the snow starts to fall. The purplish chemical will sit on the road surface and not scatter as cars drive over it, Mr. Mahoney says. This pre-wetting approach makes it difficult for the snow to stick to the streets. The solution isn’t an option in states with concrete roadways. The chemicals react harshly to some concrete variations.

Mr. Mahoney says some states — Iowa for example — work with corn-based solutions. These de-icing solutions also remain on the roads, despite car traffic, when used as part of a pre-wetting tactic and are more biodegradable than rock salt mixtures.

Robert M. Greene, sales and marketing manager for Decatur, Ill.-based Glacial Technologies, which produces corn-based solutions, says his company’s solutions work at lower temperatures than strictly salt compounds.

“With a small percentage of a corn additive, we reduce corrosion and enhance performance,” Mr. Greene says.

His company began producing corn-based solutions five years ago, but he says the use of corn began in the mid-‘90s. Adding 10 percent to 20 percent corn solution to an overall de-icing solution can bring down the freezing temperature and prevent bonds from forming, which means less chance of ice accumulating on the roads.

Some transportation departments choose not to pre-wet the roads but to treat them shortly after the first flakes fall.

Mr. Mahoney says “the trick is to get a little snow down to hold the salt. The timing is crucial … the [Virginia Department of Transportation] folks wait until just the right moment to start doing this.”

Should the road temperature fall below 15 degrees, road crews will lean upon calcium chloride, which works at lower temperatures but costs about 10 times as much as rock salt solutions, he says.

Kathy Covert, program director at the division of chemistry at the National Science Foundation in Arlington, says adding any salt into the wintry mix will reduce the rate at which water turns into ice or snowy slush.

However, Ms. Covert warns that each solution has its own peculiarities, which must be taken into account.

“Some salts will melt the ice, but they tend to attract more water,” Ms. Covert says “Your sidewalk will be always wet and will refreeze.”

Virtually all salt solutions have the unintended side effect of damaging cars, roadways and vegetation, she says.

The buildup of salt in the soil can prevent plants from absorbing nutrients and water while inhibiting plant growth. High salt concentrations in the soil also can harden the ground, making it difficult for water to seep through to the roots.

Salt also can damage concrete, but roadways are more affected by water seeping into the cracks and later freezing and expanding when temperatures drop.

Mr. Mahoney says other countries have inventive ways to deal with heavy snowfalls. Workers in some northern Japanese cities, for example, dump snow into grates built into the middle and edges of the roadways that funnel into the sewage systems and melt the snow away. The cities also use automatic anti-icing sprayers on bridges and employ some road-heating units.

Compared to those systems, Mr. Mahoney says, the U.S. roadways are stuck in the dark ages or, he suggests, the ice age.

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