A March 1 article incorrectly reported that road salt had been declared a toxic chemical in Canada. Environment Canada, a government agency, concluded that road salts are harmful to the environment and recommended that they be added to the country's list of toxic substances. But the Canadian government has not made a final decision. (Published 3/7/03)
The rock salt crystals crunching under tires around Washington came from quarries and mines and massive pools of evaporating seawater.
Tomorrow's ice-melters might come from a different source: farmers' fields.
In the battle to find the perfect way to eliminate dangerous ice, scientists are experimenting with all sorts of seemingly oddball ingredients: sugar beets, soybean husks and the soupy "steep water" that remains after tons of corn have been parboiled. They're also employing satellites, computers and high-tech road surfaces that can dispense ice-melting chemicals with the regularity of gigantic nicotine patches.
They have a simple-sounding aim in mind: "The goal behind this is to stop the snow from sticking to the road," said Wilfrid A. Nixon, a University of Iowa engineer who started his career by studying glaciers.
There's another goal as well: to reduce the amount of sodium chloride that's scattered about, lessening its negative impact on the very surfaces it's supposed to keep clear.
To understand what the future may hold, it's instructive to look at the present: Sodium chloride -- in the form of rock salt crystals -- is the ice-melter of choice around here. "Everyone uses it," said Robert Marsili Jr., chief of street and bridge maintenance for the District. At about $40 a ton, it's affordable, and it works just fine down to about 20 to 25 degrees.
Road crews play with the basic formula in different ways. In Maryland, sand is often added to provide friction. High, ice-prone bridges in Virginia get a dose of brine followed immediately by a salt and sand cocktail. Chemicals such as magnesium chloride and calcium chloride are also in the arsenal and can melt ice even when the temperature drops to10 or 15 degrees.
But any chloride compound has a dark side: its corrosive qualities and the harm that excessive amounts do to the environment. In December 2001, Canada's environmental protection agency declared road salt a toxic chemical. States in the Pacific Northwest have urged ice-melter manufacturers to create less harmful chemicals.
In the last few years, the concern has spawned such products as IceBan Ultra, Geomelt and IceSlicer, names that belie their beginnings as the leftovers of various food-related processes.
Scientists are interested in the additives for several reasons. They get rid of agricultural waste. They supercharge salt mixtures, allowing them to work at lower temperatures. One product, ClearLane, is made with cane molasses, creating tacky crystals that stick to the road surface instead of being blown away by traffic, a drawback of dry rock salt.
The main reason these products are on the market, though, is that they inhibit the corrosion caused by most ice fighters. The organic rust inhibitors aren't added to protect cars and trucks -- salt-grimed auto bodies don't turn to Swiss cheese the way they once did -- but to safeguard metal bridge decks, guardrails and the reinforced iron bars inside concrete roadbeds, which can decay after repeated exposure to road salt.
The jury is still out on these agricultural witch's brews. "We haven't found the breakthrough yet," said Dennis Burkheimer of Iowa's highway department, which is evaluating such compounds.
Many are convinced that the answer doesn't rest with what you put on the road, but how and when you put it there. Salt crystals work only after they have been moistened and mashed into the roadbed by traffic. Many experts now advocate putting down a thin layer of salty water before a single flake falls, a technique called "anti-icing."
"In the past, you let roads get slippery, you let the snow and ice pack get on the road, and then you de-iced it," said Richard L. Hanneman, president of the Salt Institute. "Now we never lose the road. It never gets unsafe."
Although it sounds counterintuitive to lay down liquid in freezing conditions, the wetter chlorides get, the better they work. (There's one drawback: The instant they get too wet, they stop working. Maryland highway officials think this may be what happened to some stretches of Interstate 270 and the Capital Beltway this winter. Maryland crews have stopped pre-treating until they find out what went wrong.)
Maryland, Virginia and other states are using other technologies, too. Hockey-puck-like sensors embedded in some highways send temperature and salinity readings to transportation department computers. If that stretch of highway isn't salty enough, more trucks are dispatched.
Two bridges on I-68 in Maryland's Allegany County are fitted with automated de-icers, nozzles mounted on the parapets and in the roadbed that dispense ice-melting chemicals. So is a ramp from Route 7 to eastbound I-66.
These pale in comparison to the measures tried in other countries. Salt trucks patrolling mountains in Italy are equipped with GPS satellite systems that are hooked into the trucks' spreaders, adjusting the flow of chemicals as the vehicle gains or loses elevation.
In Germany, highway engineers have experimented with mixing calcium chloride with asphalt itself before the roadbed is laid.
A variation is being developed in Michigan's frigid Upper Peninsula. "In real simple terms, we're looking at ways to make the pavement act like a hard sponge," said Russ Alger, head of Michigan Technological University's Institute of Snow Research. Called an "anti-icing smart pavement overlay," it's an epoxy coating put down on top of a road or bridge that soaks up ice-melting chemicals, then releases them slowly over time.
"On some bridges that are frost- or ice-prone, it could almost keep frost from forming for one winter with an application of chemicals," Alger said.
In the end, the best solution may not come from any of these techniques, but from more specific forecasts. Those in the world of ice-melting grumble that the National Weather Service is more interested in conditions in the atmosphere than on the road.
"The key thing is to begin with a forecast that works, that will tell you 12 hours before a storm begins when it's going to start and how it's going to progress," Nixon said. That would let highway crews spread loads at the right moment for maximum impact.
He said there's one final element: motorists who simply drive too fast. He's given the issue some thought.
"How do you persuade the average driver to go a little slower when there's snow on the road? One thing that seems to have a great effect is if they see a car in the ditch, they slow down. The thought arises, why don't you put cars in the ditch before it starts snowing?"
He admitted that liability problems would probably preclude such a technique.