The dangers of salt on our roads

Anyone who lives in Minnesota  appreciates the value of salt in its non-culinary form.

The massive plows that push the snow off of highways leave a layer of salt in their trail, and the crystals prevent dangerous layers of ice from forming. In Minnesota alone, more than 350,000 tons of salt is dumped on the winter roads each year, along with almost 200,000 gallons of salt brine.

While the salt creates clear roads for drivers, a new federal study shows that levels of chloride, a component of salt, are high enough in more than 40 percent of urban streams to threaten aquatic life. Urban streams carried an average of 88 tons of chloride per square mile of drainage area compared to 6 tons in streams in forests. In comparison to the 40 percent of urban streams that exceeded federal safety limits on chloride, only 4 percent of rural streams exceeded those limits.

The study from the U.S. Geological Survey also found that as the chloride levels in streams have increased as cities have turned more and more to salt to deice roads. The researchers noted that the expansion of roads and parking lots that require deicing is also contributing to the problem.

Jim Dawson reports for Inside Science News Service, which is supported by the American Institute of Physics, a not-for-profit publisher of scientific journals.

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Comments (1)

  1. Submitted by donald maxwell on 09/21/2009 - 09:50 pm.

    Remember studded tires?

    There is reason to believe that road salt use could be radically reduced if studded tires were legal again. Few people know, and probably fewer legislators remember, how the ban on studs came about. Studs became popular very fast because they had a dramatic effect on car stability in icing conditions. As stud usage headed for the million-car mark, somebody got worried and began the move to get them banned.

    I was able to get a copy of a very high-end glossy pamphlet furnished to the legislators by the Salt Institute. It presented information on a study sponsored by the Salt Institute with participation by several state highway departments. Why would the Salt Institute (members included Morton, Cargill, etc) weigh in on whether tire studs should be banned? Obviously these companies wouldn’t have bothered unless they expected that tire studs would reduce use of road salt.

    The anti-stud pamphlet highlighted pictures of roads allegedly damaged by studs, and described a “study” of stud damage on sample road surfaces, carried out in the tire test facility of the then Standard Oil of Indiana. A giant tire torture machine ran tires on the sample surfaces, with studs and without. The omission was that no sample was run without salt. But the campaign succeeded and the legislature banned studs.

    At that time, everyone could see concrete spalling from the highway travel lanes, and the idea that studs did it had appeal. Studs went away, and salt use rose.

    But within the next months and years, the same concrete spalling could be seen on the sidewalks of highway bridges, and in fact everwhere on concrete exposed to road salt. All these surfaces were well out of the reach of studs. But the impression remained that studs wrecked roads.

    Will we see the issue raised again?

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