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Posts Tagged ‘snow and ice’

Here’s a suggestion for anyone buying a 4×4. If you are prepared to spend £25,000 (or whatever) on such a fancy bit of kit, how about spending £25 or so on a tow rope?

Yesterday the weather was appalling across Kent, the southern and eastern part at least, with heavy snow, serious drifting in high winds and bone chilling temperatures. The media reports over the past 24 hours have shown a catalogue of mayhem. It is sometimes tempting to think the media exaggerates conditions but my own experience suggests that in this case they have not.

Outside my house near Ashford, the road – a minor but busy route on a sharp hill running past the village primary school – was throwing up difficulties by late afternoon. The real problems started as people began heading home from work.

One car became stuck close to the brow of the hill causing several which were following it – too closely? – to halt behind it, unable to regain the traction to get past and blocked in from behind thus preventing reversal back down the slope.

I lent my (limited) assistance and by pushing managed to get a couple of the smaller vehicles going. A Land Rover (I think it was) turned up to try and help the car at the top of the slope but without a tow rope. I hurried off to try and secure one from a neighbour but by the time I got back, the Land Rover driver had thought better of waiting and had gone, taking the driver of the stuck car with them, but leaving the vehicle itself. Therefore we had an abandoned car creating a real obstacle at the top of the hill (it would be another four hours or so until it was successfully moved).

As the evening progressed more cars, going both up and down hill, became stuck on what was now sheet ice.

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By this morning, the ice remained, as did two cars which had been stationary on the hill overnight, and the local school had closed because the headmaster – rightly in my view – had determined that it was unsafe for children to be delivered by vehicle (as many are given the large catchment area).

During earlier cold snaps this winter I thought that Kent County Council (headline on the front page of the website alongside a picture of a gritter: ‘We’re prepeared- are you?’) dealt well with the conditions, pre-treating roads and then ploughing them as the snow fell. I could not say that was the case this time round, at least from where I was standing. I understand the wind caused particular problems, particularly on exposed coastal routes like the A20, and that there are priority routes to maintain, but surely access to a school (which is only half a mile from a major A road) is one of them?

At least we should be grateful of one thing. Once again the weather has given us something to talk about.

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If the Eskimos have scores of different words for snow (in fact they don’t, apparently it is the Sami people of northern Europe who have a impressively wide vocabulary on this particular subject) then highways engineers have scores of different permutations to wade through when it comes to dealing with the white stuff when it falls on our roads.

The highway engineer’s bible on this topic is the Well-maintained Highways – Code of Practice for Highway Maintenance , Appendix H Winter Service Issues, as amended 29 November 2011.

This document is nothing if not thorough but for the layman it does not make for an easy read, full as it is of flow-charts, tables, diagrams and seemingly limitless scenarios relating to cold weather and salt.

Perhaps the first thing to appreciate is that mined rock salt (though marine salt can also be used) can be prepared by milling to two sizes, 6mm and 10mm. The difference is, well let’s refer to the manual:

“The larger particle size requires less processing and can therefore be produced faster. Thus significantly more 10mm salt than 6mm salt can be produced in the same period of time. If more orders are placed for 10mm than 6mm then the pressure on UK production has the potential to be lessened. However, smaller particles go into solution much more rapidly than larger particles; particularly in situations of low humidity. A 6mm particle size is suggested for precautionary salting, giving a faster reaction time and better opportunities for salt rate reduction, whereas 10mm is more effective for ice and hard-packed snow.”

As for the effectiveness of salt, the manual says it:

“…melts ice and snow at temperatures as low as -21°C, but below -5°C the effectiveness of the salt is reduced and below -10°C the amount needed increases to become environmentally and economically undesirable.”

Crucial to the whole de-icing process is moisture. Without some wetness the salt does not form a solution and so its melting properties are severely limited. Some local authorities pre-wet their salt but this takes time and money spent on extra equipment.

Prior to forecast snow and ice precautionary salting can take place, and then in the wake of the inclement weather ploughs skim off as much of the volume as possible before the remaining layer is again treated with salt. The danger is that it becomes too compacted for the salt to work effectively, often leaving the only practicable option of mixing grit (sand) with the salt to at least provide some extra grip on the snow.

I could go on but with the manual running to 33 pages it would take me a while and leave you overwhelmed with technical data. Suffice to say the information and instructions are out there. Whether or not people take them in is another. You, the driver can decide as you tiptoe your way around our frozen road network.

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