Glass tree road: A road in Hendersonville North Carolina following an ice storm.
Glass tree road: A road in Hendersonville North Carolina following an ice storm.Courtesy vgm8383
Its really cold where I live these days. It was 23 below zero Celsius (this is a science blog) this morning when I woke up. Bitter cold. An interesting phenomenon happens on roads when it gets this cold, a condition called black ice. It was in full effect this morning, with Twin City roads having over a dozen accidents and causing lengthy commute delays.

So, what is black ice (besides an AC/DC album)?

Black ice is a type of ice that is usually thin and forms without bubbles inside, making it harder to see. Because of its transparency, it usually takes on the color of whatever it is on, making it doubly hard to see and a hazard to drivers, bikers and walkers.

Black ice on roads is most common at night or in the early morning when temperatures are at their lowest, and before the sun has had a chance to warm the road surface. It can be mixed in with a wet road, and it can be hard to tell the difference between a road that is wet and a road that has black ice. Black ice can form more easily on bridges and overpasses as the very cold air can cool both the top and the bottom of the road at the same time, causing it to cool below freezing more quickly. Black ice can form from any source of moisture – light rain, meting and re-freezing snow or any other source of moisture on a road surface.

Here are some tips for driving on black ice. Drive safe my fellow Minnesotans – I’m going to be on the road with you this evening!

Your Comments, Thoughts, Questions, Ideas

Liza's picture
Liza says:

One big cause of black ice is car exhaust freezing on pavement when the air is this cold. Be extra careful at stop signs, traffic lights, or on metered freeway entrance ramps--anywhere cars have to idle for a while. Black ice tends to form in those areas.

posted on Tue, 12/16/2008 - 5:31pm
Joe's picture
Joe says:

You know what's interesting about that? I read articles from across North America and some even from Europe and only one, written as a sort of editorial, mentioned the exhaust as a cause. I had heard of it, and I had assumed it to be true (the exhaust has moisture...right?) but no printed "source" on black ice mentioned it. So I was wondering when I wrote this if it was an urban myth or truth - and not knowing I opted to leave it out as a cause.

posted on Thu, 12/18/2008 - 11:18am
Liza's picture
Liza says:

Huh. I just googled "black ice" and "car exhaust" together. (This post is the #1 site, by the way. Good going.) But it's followed by others that mention car exhaust as a source of black ice. Still, perhaps they're all repeating an urban myth. Where is Cecil Adams, or at least a meteorologist, when we need him/her? :)

Here are a few. Check the link above for others.

Simon Fraser University's list of winter safety precautions
BBC's h2g2 site, in which black ice is defined as frozen car exhaust

posted on Thu, 12/18/2008 - 1:30pm
ARTiFactor's picture
ARTiFactor says:

Add me to the list of those who thought black ice was due to frozen car exhaust or resulting from the condensed water that drips out of exhaust pipes around stop lights. I think I formed this opinion from direct observation.

posted on Thu, 12/18/2008 - 1:54pm
Joe's picture
Joe says:

I probably read about 10ish articles, but I didn't read any of those. I just searched "back ice"...I personally think it has to be somewhat accurate, but probably not outside of metropolitan areas?

posted on Mon, 12/22/2008 - 8:48am
Nemoudeis's picture
Nemoudeis says:

Cecil Adams (or at least one of his Minions) actually did cover this question back in 2002. He mentions automotive exhaust as a "major contributor" to the phenomenon of black ice, and goes into pretty extensive detail as to how exactly it comes out this way. You'll find it all around paragraph #7 or so.

posted on Tue, 12/23/2008 - 2:12am
maleman001's picture
maleman001 says:

I never knew about the black ice and it is cold in the morning and the night but it is hard to drive because the ice

posted on Thu, 12/18/2008 - 5:39pm
Derf's picture
Derf says:

Black ice? Where I am from, water plus cold = Ice. Thats right, ICE. I never heard of the wonderful, mysterious "BLACK ICE" till I moved to the Northwest and heard all of the local news reports trying to make everything so dramatic. " oh my god, its not ICE!!!!," " it is black ice!!!!." Total bs. Ice is ice. Get on with it .

posted on Thu, 12/25/2008 - 7:40pm
c3po's picture
c3po says:

wow !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

posted on Sun, 12/28/2008 - 3:32pm

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