2. Context
2. Context
2.1. Winter Service Provision and Policy in Scotland
In Scotland, winter service on 55,000 Kms (34,000 miles) of the local road network is provided by 32 Local Authorities (LAs). Winter service on the 3,250 Km (2,000 miles) of the trunk road network is provided by four Operating Companies (OCs) and three Design, Build, and Finance Operators (DBFOs). Under the Roads (Scotland) Act 1984 all roads authorities are required to ‘take such steps as they consider reasonable to prevent snow and ice endangering the safe passage of pedestrians and vehicles over public roads’.
To assist meeting their legal requirements each roads authority produces a winter service policy which describes what steps will be taken to maintain the local road network free from ice and snow as far as is considered reasonable. Policies vary between roads authorities and are often based on a route treatment hierarchy where priority routes have been determined depending on various factors such as traffic volumes, bus routes and access to schools, shops and medical facilities. Winter Service Policies are placed within each service provider’s website and in some cases provided also by leaflets available at Council offices. Transport Scotland places the winter service policy for each OC and DBFO on its website.
Roads Authorities’ salt stock levels are based on varying criteria such as stocks from the previous year, historical maximum usage, varying days of heavy usage and anticipated route usage in severe conditions with an allowance for a delivery period for restocking. The unpredictable nature of the winter climate means predicting annual demand for rock salt for de-icing in the UK is difficult. For some island authorities, where deliveries are made by ship, restocking can take up to 15 days or longer following placement of an order depending upon ship availability.
Weather trends can provide an indication of weather patterns over a period of years. Experience over the past decade has shown that winter has been becoming milder. It is unprecedented in recent times therefore, to have a one in 20 year weather event followed by a one in 40 year plus event the year after.
Weather forecasts provide an indication of the expected weather within any given year and cover long, medium and short range periods of time with varying degrees of reliability. Long range weather forecasts are not sufficiently reliable to enable roads authorities and suppliers to accurately forward plan salt usage in advance of winter. Medium range forecasts are more reliable but do not provide a sufficient lead in period for roads authorities to order and take delivery of significantly larger quantities of salt than normal, or for suppliers to significantly increase supplies. Short range forecasts are the most reliable but by then it is too late to mitigate against a shortage of salt. Weather forecasting cannot therefore be used as the main criteria for replenishing salt stocks either at the start of the season or when re-ordering.
2.3. Weather Conditions in the Winter of 2009/10
Throughout the winter of 2009/10 the weather conditions being dealt with were extreme; not only from a temperature and snowfall perspective, but also due to the length of time the severe weather persisted and the geographically large areas affected covering as it did the whole of the UK.
The Met Office reports indicate that Scotland had the second coldest winter since 1914, with only the winter of 1962/63 being colder. For northern Scotland, it was the coldest winter on record, with the highest number of frosts. From Thursday 17 December 2009 to Friday 15 January 2010 the UK experienced a spell of very low temperatures and significant snowfalls which affected most of the country. Daytime temperatures struggled to rise above freezing in many areas and overnight temperatures were particularly low. With little day-time thawing, fresh snowfalls added to previous accumulations and by Christmas much of the Scottish Highlands had 30 cm or more snow. Significant snowfalls continued widely at times with falls of over 30 cm in central and northern Scotland in late February. Further snowfalls persisted during March and April with only a few brief milder interludes mostly in the west and south.
The severity of the conditions led to significant disruption on the road network with heavy snowfall leading to numerous closures. Many local roads were closed or passable with extreme care for extended periods and parts of the trunk road network suffered from lengthy closures. This was even with the best efforts of all those involved to keep roads clear of snow and where closure was necessary, to re-open them as quickly as possible despite frequently working in atrocious conditions.
Case Study: The Severe Weather of 24/25 February 2010
On 25 February 2010 very heavy snow caused an electricity power line to fall across both lanes of the A9 at Auchterarder in Perthshire. About two feet of snow fell and gritters were already struggling to clear the road. The snow was widespread and the night before was no better and around 80 motorists were stranded overnight in Aberdeenshire. Heavy snow had been forecast but nevertheless the snow was quite localised with little snow in Perth or Stirling. Unlike other sections of the A9 the Perth to Stirling section has no snow gates. The Police drafted in volunteers in 4 x 4s to ferry food and drink to around 400 stranded drivers. The trunk road operating company mobilised all available winter maintenance vehicles and over 20 gritters eventually helped open the A9 after nearly 12 hours.
The severity of the conditions resulted in significant increases in salt usage, demand and ultimately the availability of supply. Using salt as a de-icer when temperatures fall below - 8 ºC is less effective, requiring an increased amount of salt used.
2.4. Salt Production and Supply
The main way to de-ice roads and footways is to spread salt on roads and footways, usually, sodium chloride (NaCl).
Salt is produced around the world by evaporation of seawater or brine from sources, such as brine wells and salt lakes, and by mining rock salt deposits. Transportation costs, lead in time for deliveries are significant factors when sourcing economic salt supplies for road de-icing purposes.
UK production of rock salt, occurs in England and Northern Ireland. The three main operational mines producing rock salt in the UK are: Salt Union, Winsford, Cheshire; Cleveland Potash, near Saltburn, Cleveland; and, Irish Salt Sales, Carrickfergus, Northern Ireland.
The main supplier based in Scotland is Peacock Salt Merchants, Ayr who act primarily as supply intermediaries between salt producers around the world and consumers. Other salt merchants and businesses which supply smaller quantities of salt have not been consulted as part of this review.
The location of producers in relation to their customers and the mode of transport used to deliver salt, combined with transportation costs being a significant component of the overall price have resulted in Irish Salt Sales serving the west of Scotland by sea and Cleveland Potash serving the east of Scotland principally by sea with limited deliveries by road. Salt Union, the smallest supplier to Scotland, serves a few authorities in the south west and central belt of Scotland.
The unprecedented requirement of salt during the winter of 2009/10 resulted in surface stocks at suppliers becoming exhausted during the winter. Suppliers within the UK are only able to mine an absolute maximum of around 12,000 to 15,000 tonnes per day. To put this in context this is only about one or two days use in Scotland in snow conditions.
Salt suppliers have indicated that they are attempting to re-establish their stockpiles from last winter while meeting customer requests to restock this summer and autumn. As a result, they may again encounter difficulties in meeting winter replenishment requirements this next winter, particularly if an early start to winter is encountered.
Winter Road Salting - Facts and Figures
- UK salt suppliers maximum production is around 12,000 tonnes/day
- 1 x 20g/m_ treatment uses 32,000 tonnes/day throughout the UK
- ‘White-out’ conditions uses 100,000 tonnes/day throughout the UK
- It takes 20 days to replenish one UK white-out day using supplies from Cleveland Potash and Salt Union mining combined
- 35,000 tonnes was the minimum recorded stock level in Scotland during the winter