[♪ INTRO]
Somehow, it’s almost winter again here in Montana, and that means icy roads.
In the United States, the most common way of battling slippery streets is with road salt.
But although it does make things safer, salt can also have long-term effects on cars,
roads, and the rest of the environment.
So a few cities around the world have thought of new, creative ways of keeping snowy roads safe.
Here are three of them, including lab-made pee.
There are a few kinds of road salt, but the most common is sodium chloride, which we usually
call “table salt”, even though about ten times more of it ends up on streets than tables.
When it’s spread on a road, the salt mixes with the water in snow or ice,
creating a solution known as brine.
Brine freezes at 5 to 10°C colder than fresh water, because the salt blocks water molecules
from easily joining together into a frozen crystal.
That keeps roads ice-free at lower temperatures, and makes ice melt sooner once the weather warms up.
With less ice, cars get more traction, so it’s no surprise that plowed and salted
roads have 50 to 90% fewer accidents than their untreated counterparts.
But states can run out of salt during especially bad winters.
And even if they don’t, salt is pretty corrosive.
If it’s not rinsed off the bottom of a car, it can eat away at the metal,
which eventually leads to expensive or dangerous problems.
Salt on roads and sidewalks can also irritate our skin and our pets’,
it can wreck our clothing, and it can be toxic for animals who eat it.
Once it washes away, it can damage ecosystems and corrode metal pipes, as well.
Salt can even corrode underground electrical cables,
ultimately releasing flammable gases and causing sparks.
In New York City and elsewhere, that leads to exploding manhole covers in the winter.
Which sounds more than a little alarming.
Although it’s usually mixed with road salt,
one common alternative to salt is sand because it gives cars more traction.
But sand clogs sewers, and is expensive to clean up.
Plus, it doesn’t actually melt ice.
Which brings us to synthetic, lab-grade pee, or, really,
a white component of urine known as urea.
Urea lowers water’s freezing point like salt does, and it’s not as corrosive
or as immediately harmful to animals.
As a bonus, it’s also a pretty common fertilizer,
so it can help some winter-hearty plants grow as it washes off the road.
Today, urea is a common ingredient in what are called “pet-friendly de-icers”,
but it might not be the best large-scale solution to the salt problem.
Even if some urea fertilizes your lawn, it can also run off into rivers, where it gets
processed by bacteria and eventually robs the water of oxygen that other organisms need to live.
So, in the last few years, companies have found other ideas, too.
For example, they’ve started marketing de-icers made of beet juice mixed with briny water.
The juice is made from sugar in the beets.
And since sugar also lowers water’s freezing point, combining beet juice with salt water
fights ice more efficiently than salt on its own.
That means it takes less road salt to achieve the same effect.
Sticky sugar also keeps salt from bouncing off the road, and it can hold it on the streets
for a few days, as long as rain doesn’t wash it away.
It doesn’t even paint the town red, like you might expect from a beet,
since sugary juice is more like molasses than you might be picturing.
It’s light-brown instead of beet-red.
And while that isn’t necessarily the most attractive snow color, its creators say it doesn’t leave a stain.
Beet juice has been used as a de-icer in a couple hundred cities and towns over the last
few years, and it’s been pretty effective.
But like urea, it’s not perfect, either.
Mixing it with brine still means using some salt, which is still a corrosive irritant.
And once it washes into rivers and streams, it can steal oxygen from the water like urea.
So another new option is cheese brine.
It’s a combination of water, salt, and the byproduct of certain types of cheese production.
And, like beet juice, it lowers water’s freezing point more than salt alone.
Although in this case, it’s because the brine is super salty, not sugary.
Also like beet juice, it stays on the road better than salt does by itself.
Companies often give the cheese brine away for free, since it means they won’t have to dispose of it.
And that saves states hundreds of thousands of dollars a year they would have spent on salt.
Cheese brine hasn’t gone through a ton of testing, so no one’s quite sure if its environmental
impact is significantly better than its competitors.
But again, the brine does still have a lot of salt in it, and it can steal oxygen from
water supplies like beet juice and urea.
And in the few counties where it’s been tested, some people do report a noticeable odor,
like you might expect after leaving a whole bunch of cheese out for a while.
So for now, salt still rules our winter roads, and cities are mostly focusing on methods
for using less of it than we have in the past.
But hopefully a better solution is somewhere over the horizon, and we just haven’t seen it yet.
Thanks for watching this episode of SciShow!
If you’d like to learn even more about the science of winter, like why ice is slippery
and what watermelon snow is, you can check out our winter compilation from last year.
[♪ OUTRO]