Black ice

General cycling advice ( NOT technical ! )
Geoff.D
Posts: 1959
Joined: 12 Mar 2010, 9:20pm

Re: Black ice

Postby Geoff.D » 3 Jan 2017, 3:45pm

The road surface itself is a factor in the formation of black ice, though I'm not totally sure of the explanation. My local parish council has just issued a warning that a stretch of road, running past the Rollright Stones in the Cotswolds, has had a number of vehicles sliding off the road. The conditions have been freezing fog recently, exacerbated by the Stones being on the top of a ridge. But the accidents have occurred only on the 500m stretch that has been recently fully resurfaced. It was billiard table smooth for riding, before the freezing weather.

I guess the explanation is as tony_s says earlier. The supercooled water droplets freeze on contact with the cold surface. But, with the surface being smooth, it's even easier for the black ice to form a continuous icy film.

whoof
Posts: 1728
Joined: 29 Apr 2014, 2:13pm

Re: Black ice

Postby whoof » 3 Jan 2017, 3:56pm

Geoff.D wrote:The road surface itself is a factor in the formation of black ice, though I'm not totally sure of the explanation. My local parish council has just issued a warning that a stretch of road, running past the Rollright Stones in the Cotswolds, has had a number of vehicles sliding off the road. The conditions have been freezing fog recently, exacerbated by the Stones being on the top of a ridge. But the accidents have occurred only on the 500m stretch that has been recently fully resurfaced. It was billiard table smooth for riding, before the freezing weather.

I guess the explanation is as tony_s says earlier. The supercooled water droplets freeze on contact with the cold surface. But, with the surface being smooth, it's even easier for the black ice to form a continuous icy film.


The section of the Bath Bristol railway path most affected by black ice is on the most recently resurfaced part and like the above it's also the smoothest. It appears it's a combination of temperature, humidity and road surface which makes predicting it pretty difficult. Then there's the out of the ordinary such as this morning where some builders had left their hose on and there was a sheet of solid ice across a path a metre wide, but at least it was easy to see. .

AMMoffat
Posts: 206
Joined: 1 Dec 2007, 1:05pm

Re: Black ice

Postby AMMoffat » 3 Jan 2017, 3:59pm

CREPELLO wrote:Wasn't the recent fatal A40 crash near Witney partly caused by black ice and freezing fog? I'm guessing that the fog froze to the road surface, causing the black ice. Question is, can you tell freezing fog from normal fog? I'm thinking that dry but untreated minor roads could become lethal if there is fog when the temperature drops.


Many (all?) modern cars have a temperature gauge that indicates the outside temperature at road level and indicate to the driver when the conditions they are driving through are freezing (fog or not) - most beep or otherwise highlight when the temperature falls below about 4C when there is a risk of ice. Whether most drivers pay any attention to this information and adjust their driving speed and style to the conditions is another question entirely.

Neither freezing fog or black ice in themselves cause crashes. Drivers failing to drive appropriately for the conditions cause crashes - failure to reduce speed being the main issue. Even choosing not to drive at all when the conditions are severe would often be a more responsible approach. And yes, I'm aware that even when all precautions are taken accidents still happen - there would just be fewer of them if drivers were more sensible.

As for cycling in icy conditions, I've fitted winter tyres (non-studded) to one of my bikes for the first time this year. Although I've yet to have the "pleasure" of riding them over black ice, or any ice at all, they are much more flexible than standard tyres in the current low temperatures so I am hopeful that they will have the desired effect when called upon.
Last edited by AMMoffat on 4 Jan 2017, 2:16pm, edited 1 time in total.

hercule
Posts: 940
Joined: 5 Feb 2011, 5:18pm

Re: Black ice

Postby hercule » 3 Jan 2017, 4:23pm

Last year I was in Glasgow for a meeting, and as I am wont to do I went out for an early morning run along the Clyde Walkway. At one point it dodges away from the river and I almost immediately found myself on a slick icy surface that I could barely stand on. At one point I had to grab the adjacent chain link fence to stop myself from flying.

I carried on in a cross-country ski-like shuffle, very cautiously, but was amazed to see several cyclists ride past with apparent complete indifference to the surface conditions. I bet they rode unicycles in their spare time! :D

I've had one bike related "off" this winter (on slick mud, not ice), plus a trip to A&E when I split my head open slipping on ice. It's made me much more cautious and probably, ironically, much more at risk of falling.

User avatar
[XAP]Bob
Posts: 16871
Joined: 26 Sep 2008, 4:12pm

Re: Black ice

Postby [XAP]Bob » 3 Jan 2017, 4:24pm

ElaineB wrote:Why risk any sort of injury? It's not pleasant riding in temperatures lower than 3* and if you ride down lanes that don't see sunlight ice can still be lurking.

Because I have to be in the office..

I use a 'bent trike, so I'm pretty confident about not falling off - my concerns are more about other road users.
If it does look like the roads will be slippery for a bit then I'll bring down the studded tyres, but they're still stowed in the garage at the moment...
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

MikeF
Posts: 3706
Joined: 11 Nov 2012, 9:24am
Location: On the borders of the four South East Counties

Re: Black ice

Postby MikeF » 3 Jan 2017, 9:57pm

hercule wrote:Last year I was in Glasgow for a meeting, and as I am wont to do I went out for an early morning run along the Clyde Walkway. At one point it dodges away from the river and I almost immediately found myself on a slick icy surface that I could barely stand on. At one point I had to grab the adjacent chain link fence to stop myself from flying.

I carried on in a cross-country ski-like shuffle, very cautiously, but was amazed to see several cyclists ride past with apparent complete indifference to the surface conditions. I bet they rode unicycles in their spare time! :D

I've had one bike related "off" this winter (on slick mud, not ice), plus a trip to A&E when I split my head open slipping on ice. It's made me much more cautious and probably, ironically, much more at risk of falling.

That's interesting. A few years ago the snow on some paths had frozen, become compacted and pocketed. Like you I could barely stand up on it. However much to my amazement I found I could cycle along it (carefully) without the bike slipping at all!
"It takes a genius to spot the obvious" - my old physics master

User avatar
NATURAL ANKLING
Posts: 10176
Joined: 24 Oct 2012, 10:43pm
Location: English Riviera

Re: Black ice

Postby NATURAL ANKLING » 3 Jan 2017, 10:28pm

Hi,
Only seen evidence of black ice once IIRC, it was the day I saw freezing rain, looks like glass, my motorcycle was covered in it.

Went out later and done a stunt I don't want to repeat on the motorcycle :o Back end went one way then the other and again but stayed on, a miracle for sure, ground looked damp but not icy.

That's the point is that you cannot distinguish it from wet tarmac.
If You Don't Try You Don't Do.....Don't Do You Don't Get...I'm Still Trying....Well Very..
You'll Find Me At The Top Of A Hill...............Somewhere...After Dark..

Vorpal
Moderator
Posts: 16840
Joined: 19 Jan 2009, 3:34pm
Location: Not there ;)

Re: Black ice

Postby Vorpal » 4 Jan 2017, 6:46am

ElaineB wrote:Why risk any sort of injury? It's not pleasant riding in temperatures lower than 3* and if you ride down lanes that don't see sunlight ice can still be lurking.
Spring isn't far away and think how fed up you would be if nursing broken bones then. A fireman once told me...'a dead hero is of no use to anyone'. Stay warm and safe until the ice has melted.

I don't risk any sort of injury; at least not more than at other times of the year. I use studded tyres when there is ice, or a high likelihood of it. I enjoy riding my bike, even when it is rather colder than 3 C. I've gone out in temperatures as low as -10.

Anyway, I live in Norway, and winter is too long to leave it until spring. Even with skiing and things like that, I would lose my fitness over the winter. It just means dressing up warm and leaving plenty of time. And it's still better than driving or taking the bus.
“In some ways, it is easier to be a dissident, for then one is without responsibility.”
― Nelson Mandela, Long Walk to Freedom

User avatar
[XAP]Bob
Posts: 16871
Joined: 26 Sep 2008, 4:12pm

Re: Black ice

Postby [XAP]Bob » 4 Jan 2017, 7:33am

I'd also guess that the prolonged lower temperatures don't lend themselves to black ice. So the surface is a bit more predictable?
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

Dave W
Posts: 1483
Joined: 18 Jul 2012, 4:17pm

Re: Black ice

Postby Dave W » 4 Jan 2017, 7:59am

"Neither freezing fog or black ice in themselves cause crashes. Drivers failing to drive appropriately for the conditions, or choosing not to drive at all when the conditions are severe, cause crashes - failure to reduce speed being the main issue"


How does 'Not driving at all' cause crashes?
Lost me on that theory.

It's called 'black ice' because it can't be seen, it doesn't tend to reflect light like frost does which makes it difficult to predict. Even if you take precautions and crawl along you are quite likely to come off. Horrible stuff.

pwa
Posts: 9616
Joined: 2 Oct 2011, 8:55pm

Re: Black ice

Postby pwa » 4 Jan 2017, 8:29am

I once came off the bike at very low speed, maybe 3mph, whilst turning right on a quiet crossroad in a residential area. No traffic, thankfully. I approached the junction slowly, almost stopping as I reached the Give Way line, then moved on as I saw there was no traffic. As I reached the middle of the road and turned right I came down with a bang. The ice was a thin film, maybe less than 1mm, and looked no different to to damp tarmac. But it was so slippery that I found it hard to stand up. It did not have the glassy look I normally associate with ice.

Thankfully there is no ice around here today so I may get a ride in later this morning.

Geoff.D
Posts: 1959
Joined: 12 Mar 2010, 9:20pm

Re: Black ice

Postby Geoff.D » 4 Jan 2017, 9:33am

Update on my previous post -this was posted on Facebook by my parish council this morning -

"Pleased to report that Highways have now agreed to include the Warwickshire section of Rollright Stones road on their gritting route in view of the recently reported problems with black ice. However, they stress that drivers have a duty to drive to the prevailing conditions."

We all know that drivers are responsible, but it doesn't make cyclists any less vulnerable whether the driver is irresponsible or simply makes a mistake on black ice. To me, black ice is to be avoided. Full stop. I ride a trike and don't worry about falling off, but I've seen the Facebook videos of trucks/vans/cars just sliding serenely down the street - inevitably using something else to stop their progress. I just don't want to be in the way (nor sliding serenely sideways myself towards a junction, etc)

https://www.youtube.com/watch?v=rtF_UiwPRYo

Boyd
Posts: 509
Joined: 24 Oct 2016, 11:56pm

Re: Black ice

Postby Boyd » 4 Jan 2017, 10:59am

I have an old bike fitted with ice tyres. If the weather is down for 3c it comes out. Got a complete wipeout cycling down steep hill, all I did was stop peddling and the bike went from under me. The temperature was supposed to be 3c. I have kalkhoff electric bike for pulling trailers, I fitted the ice tyres at the start of the winter and there staying on untill .....late February?
I don't really find the extra bit of noise that big a problem, not relative to coming off at speed.

Psamathe
Posts: 9791
Joined: 10 Jan 2014, 8:56pm

Re: Black ice

Postby Psamathe » 4 Jan 2017, 11:03am

Do studded tyres actually help on black ice ? I'd have imagined that the studs would provide extra grip by digging into the surface a bit and that resting on a hard surface they cannot dig into they might even give a lower surface area in contact with the surface. And I'd guess that black ice is hard enough not to allow studs to dig-in.

That said, I've never even seen studded tyres so may be completely mis-understanding how they provide extra grip.

Ian

pwa
Posts: 9616
Joined: 2 Oct 2011, 8:55pm

Re: Black ice

Postby pwa » 4 Jan 2017, 11:04am

I had a friend who drove his small van onto a hill that had black ice on it. He didn't mean to. Just like us, he set out meaning to be careful. He turned onto the hill at maybe walking speed, and as soon as he did that he might as well have closed his eyes because gravity did the rest. He slid to the bottom of the hill where he hit a car at the T junction. Nobody hurt. Unless we say that all motorised vehicles should be kept off roads whenever there is a risk of ice, we have to accept that there is a danger of this happening. Side roads will not be gritted and few journeys are entirely on main roads.