JohnJ80

Not entirely true - black ice is called black ice because it's thin and transparent and therefore is difficult to see. A major cause of black ice is car exhaust which contains water in vapor form which can condense it when it hits a cold roadway. It can happen on any part of a roadway and is almost not because of a car exhaust melting ice and snow. I live out in the sticks in Minnesota, and it's not at all unusual to find black ice in the wheel track part of a lane right where the exhaust would be. I have been driving on sunny subzero days on interstate highways and started to spin out when I've driven over a bridge where the roadway is especially cold. The driving trick is to get your wheels out the typical wheel paths (and away from where the exhaust would condense) onto the shoulder.

https://en.wikipedia.org/wiki/Black_ice]Black ice can also be because of fog or frost at low (road surface below freezing) temps that puts a glaze on roadways[/url]. Lots of time you'll see big crashes on the interstate that are caused by this, often in the presence of fog or a slight freezing mist at low temps. Like here as an especially dramatic example just before Christmas. I was driving in those very conditions and it didn't look all that bad. In the photos here of the interstate, you can't see anything particularly obvious.

But the tricky one in the presence of no weather issues is the black ice that forms from car exhaust condensing on very cold pavement. Typically pavement around here has some salt residue on it during the winter so if the temp is below zero for a protracted period, the salt doesn't work and can, in fact, be covered by black ice. So on a bright sunny day, all of a sudden cars may spin out or not be able to stop. That happens out this way not infrequently. Anytime it's a high traffic area either on the highway or in the city, and it's very cold, this kind of black ice can form.

Salt pretty doesn't work below about -8F and is something like 85% less effective at 15F than at 30F. MNDOT won't use it if the temp is below 15F and goes to other compounds or primarily to sand.

MinnMan

In this case, "salt" means NaCl. Combinations of CaCl2+NaCL±MgCl2 work to lower temperatures, and MNDOT switches to them when they have to, but the MgCl and CaCl2 are a lot more expensive.

Hypno Toad

Your posts is more detailed than mine (thanks) and I totally agree with all your points.

I live in Hopkins, but I have rural roots and have driven many miles on low traffic rural roads, always interesting during the sub-zero weather. To add to my background, my vehicle growing up was an old field truck (1980 Chevy), and it was rear wheel drive ... great vehicle for *****ties (AKA donuts), but also taught me a lot about controlling a vehicle with limited traction.

cyccommute 

So being a “commuter” makes me a lesser cyclist? Being only a commuter who rides to work year around for most of 45 years made me into a winter cyclist by default. Even here in supposedly winter free Denver , I’ve had to deal with ice, snow, cold, freezing drizzle, etc. I’m not inexperienced with winter…in fact, quite the opposite.

I suspect you’ll also find that a whole lot of other people who post in the Winter Forums commute as well.


And?



Who said that Minneapolis is the only place that gets cold? I haven’t. I have said that other places experience cold weather. No, not as cold as you get but even here in Denver we have cold enough weather to freeze water. We even have freezing drizzle and the dreaded “black ice”. I’ve certainly crashed on it enough.

Ummm…who’s the one getting off topic?

I’ve read dozens of similar articles and they are so similar that a case for plagiarism could be made. They all say the same thing. And they are all wrong.​​​​​​..because science! As this is actually germane to the discussion, let’s look (again) at this quote

As I said before, how much water drips out of the exhaust? And, follow up, how often? I don’t disagree that the drips can freeze when they hit the ground but the issue is one of volume. I’ve stated in posts above that the amount of water is certainly less than 50 mL. For the metrically challenged, that’s about 1/3 cup or 3 tablespoons of water. 50 mL is likely far too much but let’s go with that. How far is 1/3 of a cup going to spread in near zero conditions? 1/3 of a cup at room temperature isn’t going to spread much either even on a crowned road.

To address the “how often [does water drip from an exhaust system]” issue, it’s not going to drip every time a car stops. Once the exhaust system is warmed, the water doesn’t condense and drip out of the system but comes out as vapor. It also comes out at a much smaller quantity (5 µg/foot). Water that comes from exhaust systems at start up is likely water that was left over in the exhaust system when the car was shut off.

Let’s also address the “number of cars” issue. Let’s say that 1000 cars pass by an intersection and drip 50 mL of water each time they stop. That’s 50,000 mL of water. That’s a lot, right!? Yep. About 13 gallons. If you freeze that 13 gallons in an ice sheet 1mm (0.04”) thick, it would cover a whopping square that is a whopping 223mm wide. That’s 8”. Quite the ice sheet there.

Sure, you could spread it wider but it has to be thinner and at some point, it disappears below the imperfections in the roadway and isn’t a problem anymore. On the other hand, at 0°F or subzero temperatures, water that hits the ground is going to freeze very quickly in a thicker layer. But the thicker the layer, the less spread and, again, the water isn’t an issue…certainly not a “sheet of invisible ice”.

To be clear, I’m not “hyper-focused” on car exhaust as a “one contributing factor” of ice formation. Quite the opposite, I’m focused on car exhaust as being an very minor contributor to road ice formation. JohnJ80 posted the oft made statement that

I have looked for some scientific paper that would back this up for many years. I have yet to find any kind of research that states this. I’ve found lots and lots and lots of news articles…both print and broadcast as well as someone in a state department of transportation…that state this but there is nothing that is data backed. It is simply untrue.

As to other causes of ice, I have no problem with the way many articles describe “black ice” as forming, either by compaction and melting of snow fall or from freezing drizzle or fog. Many of the same articles that falsely claim that car exhaust is a major contributor will say something like “[black ice] generally looks like wet asphalt.”. Your own video shows exactly that. My objection is to the idea that “black ice” is invisible and/or unexpected. The road looks wet and it’s below the freezing point of water. What part of that says “oh, it can’t be icy!”?

Not just “sub-zero”. Ice (or snow) is more slick closer to the freezing point because there can be a layer of water acting as lubrication. I think it was pointed out above that ice skates work because there is a thin layer of melt water between the blade and the ice and that the colder the ice, the harder it is to generate that layer of lubrication. Your crash is very similar to dozens of crashes on ice that I’ve experienced on a bicycle while commuting (The horror!). I’ve crashed at cold temperatures but if the temperature is closer to freezing, crashing due to the wheels slipping is greatly increased.

Again, my objecting isn’t to the ice part or, perhaps, even to the “black ice” part. I object to the “I couldn’t see it” or “it was invisible” part.

cyccommute 

Please provide a scientific paper to back up this claim. I’ve looked for more than 10 years (probably closer to 15) and have yet to find one. Lots of claims by news outlets but nothing that shows actual data.
Look at the pictures again. You can see lights reflecting off the road surface. Dry pavement only reflects a tiny part of the light that shines on it. Ice (and/or water) reflects a whole lot more. The red arrow in the picture below shows the reflection of the headlamps of a truck that you really wouldn’t see on a dry roadway



The road in general looks wet. I can’t see the temperature but the report states that it is cold. Cold + water = ice. What is so hard to understand?

Again, please provide a scientific paper to back up this claim. I’m very good at finding science papers and have yet to find one that backs up this claim.

You are correct on the limits of sodium chloride. Cargill says the accepted lowest “effective temperature” for sodium chloride is 15 to 20°F.
​​​​​​​

cyccommute 

Not dissimilar to my experience. My truck was 20 years older. To add to my background, I drove city delivery for several different companies back before I got smart enough to go to college. I’ve spun many a company vehicle (both on purpose and because I was stupid) on icy road ways including a 40 foot flat bed lumber truck on freezing drizzle. I tapped the brakes on that unloaded truck and got a full 360° ride for my troubles. The world goes by very, very slowly at the end of that merry-go-round.

I knew exactly why the truck spun and never did it again. I didn’t blame it on “invisible” ice.

Hypno Toad

This Toad is a bike-commuter, but it's not part of my BF handle. So if commuter is lesser, than this Toad is lesser too.

Somebody in this thread seems to put words in other people's post that don't exist, and clear way too much time on their hands.

I mean there's this weird repeated issue of 'blaming' black ice for crashes ... the OP is talking about being a defensive rider by knowing where ice can form under different conditions. This Toad has never crashed on black ice, but I've lost traction on it. And the video in the OP is not blaming the refreeze for the crash, it's blaming a dumb Toad for leaving the winter bike at home ... the bike with studded tires.

Object all you want, but sub-zero black ice doesn't look like wet road (the way refreeze looks like wet roads); and that's the reason it's very dangerous. But feel free to ignore the article for MN media talking with MNDOT about black ice in temps below 0F/-18C... I'm sure it's just fake news.

MinnMan

Well, the thread title includes "wedge issue", so what can one expect? Some people are mighty impressed with themselves and want the rest of us to share in that glow. That my impression is the opposite may have to do with my nearly 40 years as working academic scientist. But as my grant funding doesn't depend on it in this case, I don't really care to point out the obvious distortions that are aimed at winning a debate rather than illuminating the problem

I'll do my best to avoid all kinds of slick ice and enjoy the great outdoors of the Minnesota winter.

Rock on Hypno Toad . Keep the rubber side down as best you can and make sure to post the videos when human imperfections intervene. One day we may even cross paths on the actual trail. (Oh, and good luck in the Loppet race this weekend)

JohnJ80

I’m not going to answer all of this because it’s simply pointless and a waste of time. It’s a relatively common occurrence here and we deal with it.

The only person that said it’s “invisible ice” at least with respect to my posts, is you. I said it’s “transparent” and “difficult” to see. Big difference but without much of a distinction at 65mph and when you don’t have the luxury of examining it closely while stopped.

you’re right, it *is* a matter of volume. And when you have high traffic (150,000 cars in a rush hour, for example and for sure) going over a piece of pavement that has cooled to very cold temperatures where salt no longer works with low angle sun (we’re up here at 45 latitude or higher) then there is sufficient volume and the conditions are right. it builds up slowly, it is thin, and it is very difficult to see. Don’t need a scientific paper to watch what happens in front of your own two eyes in a serious cold snap that drives temps down subzero for days.

We’re starting to see it happening again. For the last two weeks, subzero night temps and single digit day temps have been the rule and the ground temps are getting pretty far down there.

Also, FWIW, I have never seen it happen at lower latitudes. I live in Minnesota now and have for a long time, I grew up near Chicago, spent a lot of time in northern Wisconsin and Colorado. I’ve only seen it in Minnesota and in northern Wisconsin but not Chicago or Colorado.

It’s just not worth arguing with you about this. It happens, these are the conditions and you can choose to believe it or not. If you choose not to, and you come up here, in the right conditions you’ll learn the hard way how it all works. We deal with it all the time and not as a paper checking exercise.

cyccommute 

Then what did you mean by the crack “there is a commuter posting to the thread... we are certainly going to get way off topic”?

I quote extensively so that people know what I’m responding to and to avoid “putting words in other people’s posts”.

The “weird…blaming black ice for crashes” is a societal thing. People throughout the world use their lack of observation as an excuse. Even your. own video shows that you should have expected ice based on the way the pavement reflected light. I, personally, have never blamed the crashes I’ve experienced on ice on my lack of observation. I’ve been surprised by ice and have gone down hard but if the ground looks wet and the temperature is at freezing, there will likely be ice.

Again, you do know that Denver has cold weather. If that isn’t cold enough for you, we have a huge area to the west of Denver with temperatures and conditions to rival any thing you have in the upper MidWest. Antero Reservoir recorded the lowest temperature in the US this morning at -48°F.

As to your “sub-zero black ice” in that article do you mean this

That fits your definition of “refreeze” ice fairly well and isn’t something we don’t see here in Colorado as well. Or are you talking about some other article. Maybe like this one:

Amazingly, that one doesn’t mention car exhaust.

Or this one


That one does repeat the old exhaust tall tale, however. But, again, without any attribution to any kind of scientific paper.

Amazingly you can find similar stories all about “black ice” that is formed from melt water, freezing drizzle, freezing rain, wind blown snow glazing the roadway, etc. It’s almost like it’s a well known, well understood, wide spread phenomena. In other words, it ain’t all that special.

cyccommute 

Therein lies part of the problem. You up in the Midwest seem to think that you have something special that the rest of us don’t know about. It is easy to find articles from North Dakota to Texas and from Utah to Maine on “black ice”. Exactly like the kind you and your media describe.

I can find you dozens of media posts that describe “black ice” as “invisible”. Even the Wikipedia article you linked to describe it as

I don’t disagree with you that it is transparent. I disagree that it is difficult to “see”. You may not be able to see the actual patches of ice but if the road is wet and it is below the freezing point, one should at least expect ice to be present. And if you are any kind of defensive driver, you shouldn’t be driving at 65mph in conditions where ice may be present.

I haven’t seen any Department of Transportation in your neck of the woods claim that exhaust causes ice on roadways outside of intersections. There is too little water in exhaust, too much turbulence, and too many other causes for car exhaust to be any kind of major contributor on a roadway where traffic moves without frequent stops. Even at intersections there is very little water in the exhaust for it to freeze out of the air. There are other contributors that have much more influence.

What, exactly, have you “watch[ed] happen[ing] in front of your own two eyes” hen it comes to car exhaust freezing on the roadway at intersections? Car exhaust is hotter than then subzero air and while it might put out a cloud, it rises away from the cars. If car exhaust were a “major contributor” to ice formation at intersections, everything at the intersection should be covered in the same layer and thickness of ice. Street signs, benches, curbs, sidewalks, and even the walls of the building at the intersections. Anything that isn’t moving should be covered to the same thickness of ice.

You’ve never seen ice covered roadways in Chicago nor Colorado? Here’s a story from 2018 describing just about the same kind of accident as the article you linked to. In other words, a multi-vehicle crash caused by people driving too fast for the conditions.

I haven’t said that ice can’t form. Ice forming from condensation of car exhaust or car exhaust being a major contributor is just too hard to believe. You’ll have to do far more to convince me otherwise than to say “believe me”.

cyccommute 

I’m not exactly someone with zero experience in science. I worked 39 years in chemical research. I welcome you to point out “the obvious distortions”. I am fully willing to accept if I’ve made mistakes but only if you can point out where I’ve gone wrong. But I’m not going to admit any mistakes if you can’ (or won’t) point them out.

Are you really willing to accept this “car exhaust is a (sometimes, the) major contributor to glaze ice formation” idea? Without evidence? Have you looked at how much water vapor is available per gallon of gasoline burned and the distances that gallon of water is spread out over? It doesn’t bother you that there are no papers for such an extraordinary claim? I can point to at least a couple of things that have far more of an effect on glaze ice formation than car exhaust…precipitation and refreezing of melt water being the most obvious.

I do the same here in Colorado. We have ice and snow and cold here, you know. It may not be as cold but we do have some experience with winter.

cyccommute 

I made an units error in post 79. I used the wrong units and made an incorrect statement. 13 gallons (50 L) of water a millimeter thick would cover 50 sq meters. The area felt wrong when I posted it but I will correct the error here.

That does not mean that 13 gallons of water would cover that large an area. To put it in more road centric terms, a 2 lane street with parking has an 11 foot travel lane in both directions and two park lanes of the same dimensions for a total of 42 feet (13 m) wide. 13 gallons (50 L) would spread across the road from curb to curb and would be 13 feet (4 m) long. Yes that would be a lot of ice at an intersection but…

…that assumes 50 mL of water discharged from every car of that 1000 cars at the same spot and assumes that the water stay liquid enough to spread. Near 0°F, the water wouldn’t spread very far and won’t form a sheet of uniform thickness. The water would mound.

Additionally, cars don’t discharge that much water at each intersection. A cold exhaust will discharge some water but once warmed, they stop discharging liquid water and are warm enough to put out vapor instead of liquid.

Hypno Toad

Calling sub-zero black ice 'refreeze' is accurate but also very simpleminded. By this simple understand, all forms of frozen water are 'refreeze':
hail is just 'refreeze'
glaciers are just 'refreeze'
lake ice is just 'refreeze'
... even snow is just 'refreeze'.

Expanding on this point, snow is snow is snow, right? Unless your a ski resort. Then you have as many as 65 terms for different snow conditions. This person from CO likely knows that, since they are in a state that has a massive industry focused on snow sports (it's estimated that CO generates $4.8 billion from the snow sport industry). I would love to see this commuter tell a CO skier that snow is just snow and there's no need for specific terms.

Hypno Toad

I know that Denver gets cold, and I know that Minneapolis gets colder and STAYS colder. I know that the two cities are not the same climate.

High altitude CO gets cold, Northern MN gets cold too ... and how does this apply to the topic?

But hey, here's my buddy Justin, he just finished the Arrowhead 135, he posted this picture ​​from Embarrass, MN.



(The thermometer might be inaccurate or he's in a low place colder than the local weather station which is 5 miles away at an airfield ... official temp yesterday was -38F)

rumrunn6

hope his face didn't freeze like that!

Hypno Toad

Having ridden countless miles with Justin, I'm sorry to say his face froze like that years ago

djb

Funny guys
But geez Louise that's effing cold. I think the coldest I've been out in was -35c .
I have downhill skied at -30c and with the wind speed going on it was pretty dire.

Really can't imagine biking an endurance event with -20, -30, -40c temps. That really adds a challenge of just managing all the various aspects of your clothing properly over such a long period, not to mention fueling and hydration.

JohnJ80

You may want to sit down for this - I dont give a rip whether I've convinced you or not. we deal with this all the time.

FWIW, I've also spent a lot of time in Colorado in the mountains in all kinds of conditions and that includes a lot of snow and ice on roads. Colorado ice isn't nearly as persistent as ours is because we don't have as much sun nor is it as strong.

But hang in there - its a unique obsession you have there.

Hypno Toad

This post wins ^^^^

djb

In our neck of the woods, intersections get glazed and super icy and I'm fairly certain that it's from the braking action friction that goes on.
Kinda like ice skates, apparently the pressure of the blade on the ice melts the ice for a fraction of a second and reduces the friction between blade and ice.
Cars constantly braking, and sliding locking up , must be a factor at intersections. You learn early on (after sailing through a stop sign) to be really damn careful of this. Years ago a neighbour was pushing her baby in a carriage and someone slid through and bumped into the carriage, all was ok, but both of them weren't watching enough.

here they salt and grit the crap out of intersections. Works, but boy it's tough on cars over the years. And my bike too-why I wash it after every ride.

MNBikeCommuter

I was really planning on staying out of this but... <heavy sigh>

What would be helpful is to identify the source of water if it isn't from car exhaust. What are we (drivers, weatherfolk, scientists, etc.) missing? We have seen for decades ice form in the wheel tracks on the freeways in MN during rush hour on days below 0F with no wind and no blowing snow and no frost because the dew point is many degrees colder and no snow getting dragged onto the freeways from side streets because they are dry too. We don't see ice form in the wheel tracks when traffic is moving at normal speeds. But if there's a slow down because someone did something stupid, or people continue to show they can't successfully merge onto the freeway, or..., we see ice form. Why?

I suspect, but have no proof or research to validate my suspicions, that there are fewer incidents of such ice forming now than when I moved to the Twin Cities 33 years ago. Possible reasons for this could include more SUVs and other vehicles with higher clearances and hence exhaust pipes farther from the roadway, plus the old passenger cars used to direct their exhaust downward whereas now the tailpipes are straight, etc.

cyccommute 

I have not said they are the same climate. But they do have similar conditions. We deal with ice, snow, snowmelt, water that freezes, etc during the winter months. We even deal with subzero temperatures. Yes, it gets cold in the upper Midwest but you really aren’t unique.

cyccommute 

What would be helpful would be to show a scientific paper measuring…with real data…this loopy idea. If someone at a department of transportation says “car exhaust is the major contributor to black ice at intersections” what are they basing that on? If they have a scientific study they can cite, I have yet to find it despite several years of looking for one. If this were the case there would be some study from the University of Wisconsin or the Planck Institute of Black Ice Studies or some other organization.

Also note that the statement is about ice at intersections. I’ve never seen any one say that ice on open roadways comes from car exhaust. At an intersection, a car driving down the road moves a whole lot of air which would stir any car exhaust moisture into the air around it. At highway speed, there is even more stirring of the air. Any moisture produced by a car (or multiple cars) would mix with moisture in the air. The atmosphere has far more moisture in it than the car exhaust and is actually the major contributor to ice formation.

The temperature of the exhaust also has to be considered. Exhaust from an engine is warmer than the surrounding air and moves upward. Add that to the stirring action of the car moving through the air and the exhaust is swept upward away from the roadway.

There are many more sources of water for ice formation that are readily available than car exhaust. Every news article I’ve read from the upper Midwest…and I’ve read hundreds of them…states something similar to this


I have no problem with that definition nor with the most of the conditions that they say cause ice to form. (They have an interesting take on the “car exhaust” idea which I don’t agree with.) Those kinds of conditions exist in about 90% of the US and that kind of ice can form just about everywhere except southern Arizona and southern California. I’ve crashed numerous times on that kind of ice here in Colorado over 45 years of bicycle riding and commuting.

I don’t even have a problem with calling it “thin [and] transparent”. It is. I just have a problem with people saying that it is “invisible”.

cyccommute 

Those are 65 terms used by the cool kids. Us regular folk certainly don’t go around calling snow “pow-pow”.