On Sun, 07 Jan 2018 20:30:21 -0500, Radey Shouman
wrote:
Frank Krygowski writes:

On 1/7/2018 1:28 AM, Sir Ridesalot wrote:
Just wondering if when it's known that there can be black ice on the
roads if anyone here wears a helmet or other protection (such as
elbow pads) that they'd not normally wear when the roads are clear.
Do you?

Well, "it's known that there can be black ice" sounds to me like
"It's near or below freezing."

Surely you need two things for black ice: freezing temperatures and
liquid water. Hoarfrost isn't black, neither is snow. To get
transparent ice on a reasonably crowned road you need quite a bit of
liquid water, so I expect black ice when snow melting temperatures are
quickly followed by temperatures well below freezing.

That's not black ice, that's regular ice.

Black ice is visually transparent, usually formed by condensed moisture
in vehicle exhaust freezing to the roadways. The road can be otherwise
dry without a visual clue. It's more prevalent on bridges because those
road surfaces are colder than roads on top of the ground. Usually this
is a phenomenon that happens below 0F or about -20C, at which
temperatures crystal salts or brines tend to have little benefit.

Here in Minnesota and over by Madison where Andrew is, we get those
conditions multiple times most winters. Since there is no visual cue to
its presence, the first hint is often that vehicle up ahead slewing out
of control... if you're lucky and it's not the vehicle next to you- or
your vehicle. Drivers around here just know to beware when the temps
are down to 0F- it's one of the ways to spot the newbies, too.

I remember driving from Chicago back to Minnesota many years ago as a
young driver. I was on I-90 in the middle of Wisconsin on a bitterly
cold late afternoon; between Madison and the Dells. No snow cover yet,
just danged cold and not a sign of ice on the road. I drove onto a
short three lane bridge with a curve; started out in the inside lane and
a second later was exiting the bridge in the outside lane- white as a
sheet and with eyes like saucers, I'm sure. It was sheer luck I didn't
park it in the guard rail and that there weren't any other cars anywhere
near me.