Monday, 11 December 2017

It's Snow Joke

Many parts of the UK get snow each Winter, but being a Londoner, it's a novelty for me and Sunday's sprinkling got me thinking.

With any significant snowfall in the Capital, the place grinds to a halt, although being a big place, it seems that north of the river was more affected and certainly out on the edge we had plenty (being on higher ground). By Monday morning, the rain had washed most of the snow away to leave one wondering about what all the fuss was about!

As it was a Sunday morning, fewer people were out and about than on a weekday. At least early in the morning, it wasn't too bad under foot and the kids took advantage to give the sledges a rare outing. Sadly, some of the people driving didn't see the need to slow down and we got sprayed a couple of times by the slush - is it a 4x4 owners' mentality that they are truly invincible?

We walked to the local shops (well Mrs RH and one of the girls did, my boy and youngest daughter made it half-way before she decided she was too cold!). 

My wife was chatting to a lady who just got off the bus as we passed the stop - there were 40 minute delays and being a carer who didn't drive, it was going to be a tough day. 

We spent the rest of the day indoors. Twitter and the news bulletins kept us up to date with the transport problems across London. Of course, there were plenty of pundits going on about how council's had been caught out, but this simply wasn't true. The problem was that heavy rain in the early hours would have washed away any salt and a lack of traffic on a Sunday would have meant a lack of traffic-action.

I should perhaps explain that "gritting" is actually the application of rock salt rather than "grit", although in some cases sand is used (often pointlessly). The use of salt on an already-frozen highway surface will melt the ice (pre-salting) and when applied before freezing temperatures occur, it will lower the freezing point of water. Many local authorities use an additive to make the rock salt sticky which is a byproduct from the sugar refining and livestock feed industries.

The problem with snow-fall is that unless extremely light, pre-salting can be overwhelmed and when the snow has fallen in any decent accumulation, gritting just won't melt the snow. If we then get into snow clearance, we need a much thicker layer to make the use of snow-ploughs viable. Because of the rarity of snow at that depth in most parts of the UK, ploughs are an expensive piece of kit to have on the off-chance (although some gritting lorries can have a small plough attached).

Where there is a layer of ice or hard-packed snow, then actual grit can be added to the rock salt to help break up the frozen layer and provide some traction. the problem with all of this is the salt is highly corrosive and can attack vehicles. Many large bridges will be treated with de-icing chemicals to reduce the risk of salt attacking reinforcement.

Footways and cycle tracks are a different matter. The use of rock salt requires the wheel action of traffic to make it effective it crushes the salt which mixes with water to form brine. Foot and cycle tyres cannot crush the salt and so a brine solution can be sprayed onto surfaces to either stop ice forming, or to help melt it. There are some places in the UK where this is deployed (especially on cycle tracks) because regular low temperatures and decent cycleways make it worth investing in the kit.

Where snow and ice have accumulated on footways, the best way to get rid of it is to get out with shovels and clear it, followed by the application of brine, or fine salt (so long as the wind doesn't blow it away). The official advice is here and to be honest, it is unrealistic to expect local authorities to have the resources to get into every side street and so clearing the area outside of where you live or work is a really helpful thing to do. The local authority will have hierarchies for treatment, but main roads and bus routes will be the priority. 

The whole approach to dealing with winter weather on the highway network is known as "winter service". It's essentially planning an then implementing a strategy to keep people moving. Low temperatures form the main thrust of a winter service plan, but snow certainly features (even in London) and increasingly, dealing with flooding is becoming more prevalent.

The future is going to be interesting. Climate change experts suggest that weather will become more extreme and so in the UK, we might expect more storms and rain leading to flooding. Also, it could mean that heavy snowfall occurs and places which are not usually used in dealing with it will have greater disruption. 

How we use of road network will also change. Sunday's snow made me wonder if autonomous vehicles would have coped. There is a debate raging about how AVs will navigate and how they will deal with people outside of the vehicle. There are discussions about how AVs will use a combination of GPS and on-board sensors. The trouble is that GPS is not perfectly accurate and sensors could be disrupted by snow and indeed heavy rain or fog. It is a world of difference between a sunny, dry Californian motorway and a snow-covered local UK street with parking on both sides!


  1. That's an interesting thought about autonomous vehicles as I hadn't considered the effect of cold weather conditions on their performance.

    Presumably they will be programmed to drive slower when there's a risk of ice or snow - if they rely on sensors to identify that they're driving on ice or snow, then it's probably too late - but how do they cope with identifying lane position when it's hidden under an inch or more of snow?

    Thanks for the info about clearing/treating icy paths and roads though. This is stuff I've heard before, but it's always handy to be reminded, especially given we don't have to worry about it very often in the south of England!



    1. I must admit, I hadn't given it a moment's thought before. It's going to be really challenging - I wonder if the cars will "refuse" to drive if it is bad?