My wife originally hails from Minnesota,
where snow comes in November and stays there until April. Alas, the move to
upstate New York was not much of an improvement…
If you're from a place that gets hit hard
in the winter, you know how important clear roads are when you need to travel.
Plows, salting, and sand are tools we use to clear the roadways and make them
safe and driveable during and after winter storms. But at what cost? Do our
roads need a salt diet?
Road salt, sodium chloride (NaCl), has
been a go-to method for de-icing roads. It's relatively inexpensive,
natural (normal road salt comes from mined rock salt), and lightweight - all
good things. What's not so good is how much we use - around 22 million tons
lace the nation's roads every year. And all that salt doesn't just disappear.
Much of it is finding its way into nearby groundwater, lakes, and streams, as
evidenced by rising salt levels in U.S. freshwater bodies over the years. Salt
concentrations along some roadways have been found high enough to hamper nearby
aquatic life and plants.
Typical road salt contains about 40%
sodium (Na+) and 60% chloride (Cl-) by mass. Chloride is completely soluble can
easily find its way into soil, groundwater, and surface water, which at high
concentrations can be toxic to plants and aquatic organisms. Sodium, though not
as mobile as chloride, can disrupt the balance of nutrients in soils and
affect the quality of surface and groundwaters. Wildlife (especially birds) can
also be harmed from the ingestion of salt granules or from drinking water
runoff from the roads. Additives to road salt (like ferrocyanide for
anti-caking) and impurities like iron and phosphorous can also impact the
environment and human health.
There are other, more noticeable costs
besides impacts to the environment. Probably the biggest of these is vehicle
and infrastructure corrosion. Chloride corrosion deteriorates everything from
concrete on roads and bridges, to power utility lines, to the under-carriage of
your beatiful new car. Salt corrosion causes billions of dollars in damage each
year. But such are the costs of the need for clear roadways.
Some alternatives to normal road salt,
which can effectively melt ice at or above 15degF, include calcium chloride
(melts to -20degF), potassium acetate (-15degF), and magnesium chloride
(-10degF). Unfortunately, they are usually more expensive than road salt, and
some are just as corrosive and environmentally harmful. Preventative strategies
can reduce the overuse of road salt, such as anti-icing (spraying salt
solutions on roads before a storm) and pre-wetting the salt so it sticks better
on the roads. Road crews also need to determine the point at which more salt does
not equate to better roads. The goal is to use less salt to achieve the same
performance.
Our expectations for clear roadways are
clearly very high - how quickly after a major snowstorm do you expect the roads
to be cleared? How often do people drive in bad weather when they shouldn't?
Has our culture become too demanding? Maybe, maybe not. Regardless, we can
always look to make our winter-fighting strategies smarter and more efficient.
And if you're from Minnesota, New York, or
any other winter weather place, Merry Christmas and please drive safe this holiday season. If you're from Florida, buy me a plane ticket.
Sources:
Minnesota Pollution Control
Salt's Effects Prompt Tech
Alternatives - Discovery News
Impacts of Road Salt - NH DES
Winter Road Maintenance
Practices - ODOT
Winter road image via WCNC
Salt & plow image via MN PCA
Road salt image via NH DES
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Re: Winter Roads & the Salt Diet
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