Winter Service Operational Plan

Following receipt of the forecast the Duty Engineer will assess the risk across the network, referring to the decision matrix and instruct any action on a route-by-route basis. Other factors that may be considered include the residual salt level and the local effects of known frost hollows, bridge decks etc. on the road surface.

Precautionary salting for ice and frost will be instructed on a route basis and be carried out at a rate detailed in section 25.

The timing of precautionary salting is dependent upon the prevailing weather conditions and will be arranged to ensure the network is treated prior to the formation of ice and frost.

Deploying the necessary Management and Operational Resources

(i) Council Emergency Centre  

Should the Extreme Weather Event Board decide to open the Emergency Centre this will be manned as follows:

• ITS Engineer
• Highways Operations representative
• Duty Engineer
• Communication Officer (between 6am and 6pm)
• Appropriate number of support staff

(ii) Dorset Direct Call Centre

During normal working hours an experienced highway officer will establish a link with Dorset Direct to offer the necessary specialist operational advice and guidance.

(iii) Operational Depots

Operational management will be located within three “control depots” under the direction of a Duty Supervisor.

These depots will be Gibbs Marsh, Charminster and Ferndown and each will be staffed over 12-hour shifts by a Duty Supervisor and a highway support officer.

In addition, a team of “spotters” will be deployed from within the Community Highways teams to patrol the network and provide condition reports directly to the Duty Supervisor within the control depot.

(iv) Drivers and Associated Operatives

Prior to any extreme weather event, the Service Manager for Network Operations will convene a meeting with operational managers to compile the necessary staffing rotas to ensure a 24 hour resource plan is in place.

These rotas should be published 24 hours before any event to ensure those involved have sufficient notice and any necessary personal arrangements can be made.   

Ploughing is the most effective method of dealing with snow and ploughing should aim to completely clear the snow from the road surface.

Before snowfall a 40g/m² pre-treatment will take place across the entire precautionary salting network. This will provide a de-bonding coat of salt which should assist future ploughing operations.

Ploughing should commence as soon as is practical on the network, where conditions allow. Each pass should be supplemented by salt or salt / grit mix with a spread rate as shown in section 25.

In urban areas, where ploughing is impractical, repeated applications of salt / grit mix can be used to remove heavy accumulations of snow. This practice should not be used where ploughing is possible.

During repeat actions the salt may be supplemented by grit – see section 25.

During prolonged snowfall it may be necessary to plough continuously to prevent build up and compaction of the snow by traffic. However, once the depth of snow exceeds 100 – 120mm, or on steep gradients, it may be necessary to plough without salting to aid traction.

Following a forecast of settling snow the community link network will be pre-salted at 20-40g/m² dry salt.

After snow, the network will be ploughed and salted as soon as resources become available, either by Dorset Highways or by nominated contractors. Repeated ploughing and salting will take place when resources are available.

23.1 Priority Ploughing Routes:

During very heavy, prolonged, and county wide snowfall it is not normally possible to keep all the precautionary salting routes free from accumulations of snow. It is therefore necessary to focus resources on key routes. The need to run two vehicles on these routes, one to clear snow and the other to treat by spreading salt/grit, reduces our capacity to treat the entire network. The aim should be to keep these priority routes clear and once achieved to move onto clearing the rest of the precautionary network.

Extra resources, such as ploughing contractors, should be deployed at the earliest opportunity to assist in clearing these routes.

It is accepted that, at times, some of the precautionary network may become impassable but by concentrating on principal routes some traffic movement can be maintained.

23.2 Other Routes:

Other routes will be ploughed and treated as directed by the Duty Engineer.

When heavy snowfall is expected to affect the County the Extreme Weather Event Board will establish a Control Centre in the Emergency Centre at County Hall.

The Control Centre Team will liaise with the Operational Teams, Traffic Team Leader, Emergency Services, Dorset Direct, Communications Team, Duty Engineer and other officers as required.

The Control Centre Team will be responsible for:

• maintaining a diary record of the event
• entering road closures / reopening information on Travel Dorset
• issuing condition reports to media via Communications Team
• issue direction regarding snow clearance priorities
• liaise with adjacent Authorities to co-ordinate cross boundary clearance
• liaise with Dorset Council Emergency Planning regarding stranded drivers, local emergencies, requests from emergency services

In the case of widespread disruption, the Dorset Highways ‘Emergency Planning Liaison Officers’ will act in a co-ordinating role with Dorset Council Emergency Planning.

The decision-making process used by Dorset Council follows recommendations issued by the NWSRG.

25.1 Road Surface Wetness:

For the purpose of allocating treatments, a distinction is made between dry, damp and wet road surfaces. The following definitions should be used when making the treatment decision:

25.2 Precautionary Treatment Decision Matrix:

A decision matrix for precautionary treatments based on road surface conditions and predicted weather conditions is given in the tables below.

The decision to undertake precautionary treatments should be, if appropriate, adjusted to take account of residual salt or surface moisture.

All decisions should be evidence based, recorded and require continuous monitoring and review.

Notes:

a) Particular attention should be given to the possibility of water running across carriageways and other running surfaces e.g. off adjacent fields after heavy rain, washing off salt previously deposited.

b) When a weather warning contains reference to expected hoar frost, considerable deposits of frost are likely to occur. Hoar frost usually occurs in the early morning and is difficult to cater for because of the probability that any salt deposited on a dry road too soon before its onset may be dispersed before it can become effective. Close monitoring is required under this forecast condition which should ideally be treated just as the hoar frost is forming. Such action is usually not practicable, and salt may have to be deposited on a dry road prior to and as close as possible to the expected formation of frost. Hoar frost may be forecast at other times in which case the timing of the salting operation should be adjusted accordingly.

c) If, under these conditions, rain has not ceased by early morning the action should be initiated as rain ceases.

d) Under these circumstances rain will freeze on contact with the running surfaces and full precautionary treatment should be provided, even on dry roads. This is a most serious condition and should be monitored closely and continuously throughout the danger period.

e) Weather warnings are often qualified by altitudes in which case differing action may be required for each route or from each depot.

f) Where there is a hint of moisture being present a pessimistic view of the forecast should be taken when considering treatment to negatively textured surfaces.

25.3 Traffic Levels:

For the purpose of allocating treatments four levels of traffic flow are defined.

Spread rates in the provided matrices assume heavy or medium traffic.

If the traffic level rate is known to be low or congested, then rates should be increased by 25%.

Congestion should be expected when spreading between 7:30am - 9:30am and 3:30pm - 6:30pm.

25.4 Determining Salt Coverage / Spreader Capabilities:

For the purposes of decision-making, and when using table 4 below to determine spread rates, Dorset’s gritting fleet is generally regarded as having ‘Good’ coverage.

Where salt is taken from uncovered stockpiles, then ‘Fair’ coverage should be selected in determining spread rates for the routes affected.

25.5 Salt Loss:

Wind speed and direction can affect the spreading of salt and, in dry conditions, also affect the length of time that the salt will remain on the road surface. When practical, it is therefore recommended that we avoid spreading during the predicted high wind period, i.e. periods when mean wind speeds are predicted to be 20mph or more.

This issue is likely to affect some locations on the salted network more than others, and the precise effects of high winds are difficult to quantify due to the nature of the wind field close to the road surface and the number of variables involved which include, amongst other factors, the direction of the wind field relative to the salting vehicle and the grain size of the salt etc.

It should be taken into account that forecast mean wind speeds typically relate to those at a height of 10 metres above the ground and these are not likely to be the same as those closer to the ground and care should be taken when comparing wind data from Road Weather Information Systems (RWIS) to forecasts.

When treatments are carried out during high wind conditions, Duty Engineers will monitor residual salt levels and carry out re-treatments if and where necessary. If this issue is considered to pose a significant risk, spread rates should be increased by 25% when carrying out precautionary salting operations during periods when forecast mean wind speeds are 20mph or higher and roads surfaces are predicted to be dry.

25.6 Spread Rates for Precautionary Treatments:

25.6.1 Forecast Frost Conditions:

The following points must be considered when using the spread rate matrix:

a)   The given rates are for sections of well drained roads without ponding or runoff from adjacent areas.

b)   The rates may be adjusted to take account of variations occurring along routes such as temperature, surface moisture, road alignment and traffic density.

c)   The rates may be adjusted to take account of residual salt levels. However, residual salt levels will tend to be lower if lower spread rates are introduced. Residual salt levels are most likely to be significant on marginal nights after treatments on two or three successive days without precipitation in the intervening period.

d)   All decisions should be evidence based, recorded, and require appropriate monitoring and review.

e)   During periods of sustained freezing, if surfaces are well drained and if there is neither seepage (from melt water) nor ice present, rates of spread for treatments carried out within six hours of previous treatments may be 50% of the rates stated in the matrix.

Important note: When using salt from uncovered stock-piles the minimum spread rate must be 15g/m².

25.6.2 Treatments for Snow, Ice and Freezing Rain:

• It is impractical to spread sufficient salt to melt anything other than very thin layers of ice or snow.
• Ploughing is the only economical, effective and environmentally acceptable way to deal with all but very light snow.
• Ploughing down to the road surface is preferred. However, snow ploughs should be set to avoid risk of damage to the plough, the road surface, street furniture and level crossings.
• Ploughing to the road surface minimises salt usage and makes salt treatments more effective.
• Drainage should not be obstructed when ploughing. Windrows or piles of snow should be removed or be positioned to allow melt water to reach the drains. If necessary, piles of snow should be removed so that melted snow does not overload the drainage system or run back onto the road.
• Windrows should be removed or ploughed back when further periods of snow are anticipated. This will provide space to plough further snowfalls.

25.6.3 Preparation Before Ice and Snow:

To prepare for and facilitate ice and snow treatments the following should be considered:

• when snow is forecast, ploughs should be prepared, and contractors placed on stand-by in order that snow clearance can start without delay as and when required
• to facilitate the breakup and dispersal of ice and snow by traffic, treatments must be made before snowfall and freezing rain so that sufficient de-icer is present on the surface to provide a debonding layer
• although it will increase salt usage before snowfall and where practicable, consideration should be given to spreading salt on as much of the network as possible (i.e. beyond the precautionary and community networks). This will provide a debonding layer and facilitate the breakup and dispersal of snow by traffic in areas where subsequent treatments may not take place for some considerable time or at all

25.6.4 Depths of Snow:

This guidance defines two main snowfall categories – light snow and moderate / heavy snow.

The highest practicable spread rates are considered to be 40g/m² of dry salt. When combined with the action of traffic this is sufficient de-icer to melt snow depths which are equivalent to 1mm of water at temperatures down to -2°C. Generally, there is approximately 1mm of water in 5mm depth of wet snow, 10mm depth of ‘normal’ snow and 15mm depth of dry, powdery snow.

In this guidance ‘light’ snow is taken to be snow equivalent to 1mm water (or less) while snowfalls equivalent to more than 1mm are considered to be moderate / heavy.

Note 1: Were time constraints dictate, a treatment of 20g/m² across the whole of the scheduled network before the commencement of snow or freezing rain is more advantageous than 40g/m² on only part of the network.

25.6.4 Treatment During Snowfall:

Ploughing should start and, where practicable, be continuous to prevent a build-up of snow.

On roads with heavy traffic, it is preferable to prevent a build-up of more than 10mm depth of snow, whereas the build-up should be no more than 50mm depth where there is a risk of compaction by traffic.

Plough to remove as much material as possible (e.g. slush, snow and compacted snow).

Ploughing should be as near as possible to the level of the road surface.

Note 1: During and after snowfall, only the ploughed lane should be treated if other lanes have still to be ploughed. The spread width settings should be adjusted accordingly.

Note 2: A de-icer should not be spread alone without abrasives to anything other than a thin layer of ice or compacted snow when snowfall has ceased, or future snowfall will be less than 10mm.  Applying salt alone to compacted snow and ice can produce dangerously slippery conditions if a weak brine film is formed on top of the ice/snow layer.

25.6.5  Treatment when Slush is on the Road (and May Refreeze):

It is important to remove as much slush as possible by ploughing to reduce the amount of material available to form ice when temperatures drop, as well as to reduce the amount of salt required for subsequent treatments.

We will: 

• plough to remove as much slush as possible, as near as possible to the level of the road surface
• spread: 40g/m² of dry salt (See Note 1) after removing slush

Note 1: After snowfall, and when there will be no further ploughing but some slush remains on the road surface, it may be necessary to change the settings normally used for precautionary treatment to ensure a satisfactory distribution is achieved over the target spread width.

25.6.6  Treatment when Thin Layers of Ice (Up To 1mm) Have Formed:

When a thin layer of ice has formed, including freezing rain the following treatment should be made:

Note 1: Abrasives should ideally be 5-6mm and angular, but gradings down to 1-5mm should be reasonably effective. After abrasives have been used drainage systems should be checked and cleared if necessary. Recovered material, which will be contaminated with road oil, must be disposed of safely.

Note 2: Care is needed when salt is mixed with abrasives with high moisture content. Checks should be made that the mixture remains free flowing, does not clump and can be spread effectively.

25.6.7 Treatment for Thicker Layers of Ice or Compacted Snow:

When thicker layers of ice have formed, including freezing rain, the treatment should be as follows:

Plough to remove as much material (e.g. slush, snow and compacted snow) as possible from the top of the compacted layer.

Note 1: For medium thicknesses of compacted snow and ice, treatments without abrasives should only be used when earlier precautionary treatments have successfully established a debonding layer, and there is sufficient traffic to break up the layer of ice quickly.

Note 2: For high thickness of compacted snow and ice (greater than 5mm) treatments with a significant amount of salt should not be considered because they may leave the surface uneven. Any brine formed on the surface may collect in hollows and deepen them further, which can lead to a very uneven surface.

Note 3: Abrasives should ideally be 5-6mm and angular, but gradings down to 1-5mm should be reasonably effective. After abrasives have been used drainage systems should be checked and cleared if necessary. Recovered material, which will be contaminated with road oil, must be disposed of safely.

Note 4: Care is needed when salt is mixed with abrasives with a high moisture content. Checks should be made that the mixture remains free flowing, does not clump and can be spread effectively.

Note 5: When there are layers of snow, compacted snow, or ice of medium or high thickness on the road surface, it may be necessary to change the settings normally used for precautionary treatment to ensure a satisfactory distribution is achieved over the target spread width.

Note 6: A small amount of salt should be added to the abrasive to prevent freezing of the water within it. If the moisture content of the abrasive is 7%, 25g per tonne of abrasive is sufficient to prevent freezing if thoroughly mixed.

26.1 Salt Stock Control:

Throughout the winter period the salt stock control spreadsheet (located on the Winter Service and Emergency folder on the highways computer server) is to be updated daily following an action.

26.2 Forecast Monitoring:

Throughout the winter period the minimum forecast surface temperatures for each domain, route and the actual minimum temperatures recorded by the 11 weather stations are to be recorded daily this information will be held by are forecast provider on their systems. Due notice is to be given to any revision in forecast. This information will be used by the forecast provider to assist any future modelling of the weather domains and route optimisation.

Regular meetings are to be held with the forecast provider throughout the winter season to monitor the forecast performance.

26.3 Decision Monitoring:

The Action Decision made by the Duty Engineers will be monitored independently against each of the route forecasts. This work will be carried out by the Forecast Provider.

26.4 Route Compliance Audit:

The Senior Agent will audit routes utilising our vehicle telematics software throughout the winter season. This will be logged on the Highways Computer Server or SharePoint.

27.1 Operational Staff:

All operational drivers will hold City and Guilds Unit 6159 Winter Maintenance Operations and will receive refresher training on a five-year frequency. Those drivers in the process of training towards the City and Guilds qualification will be assessed for competency based on the criteria of Unit 6159 by a competent person. All those involved in the winter maintenance service will attend part or all of the Dorset Highway winter service dry run induction day.

New operational drivers will be shadowed by an experienced driver until such time as they are deemed competent and are confident to carry out treatment routes unaided.

27.2 Duty Engineers:

Duty Engineers will receive training in basic winter road forecasting and advanced winter road forecasting by the current winter forecasting provider, prior to first carrying out winter service duties. One to one mentoring of new Duty Engineers will be carried out until they are sufficiently competent to carry out the decision-making duties on their own. The Duty Engineers will receive refresher training in advanced winter road forecasting on a five-year basis unless specific training need is identified. Duty Engineers will undertake the IHE winter decision maker accreditation within a reasonable period.

Following the release of the Code of Practice “Well-Managed Highways Infrastructure” our adverse weather plan now covers all weather impacts on the highway network and does not just concentrate on snow and ice. Sections include:

• flooding
• high winds
• heat
• cold temperatures and snow

This document describes Dorset Council’s arrangements for dealing with adverse weather on the highway. It also provides contact information for key personnel.

1.2 The plan covers arrangements for roads and structure in Dorset that are the responsibility of Dorset Council. It excludes arrangements for roads that are the responsibility of the National Highways, i.e.

• A35 Bere Regis to Lyme Regis
• A31 Bere Regis to Ringwood
• A303 at Bourton

1.3 General description of service

Dorset Council (DC) is committed to providing a robust adverse weather service including responding to winter and other adverse weather conditions. The adverse weather service is provided internally by DC through Dorset Highways. The extent of the service provided will vary depending upon the severity and nature of adverse weather conditions and resources availability.

1.4 Objectives

DC aims to safeguard the travelling public from the hazardous effects of snow or ice or other adverse weather conditions so far as it is practicably able to with the resources available. Proactive winter maintenance and other emergency operations will normally be undertaken based upon available weather forecast information, knowledge of prevailing local weather conditions and resource availability.

1.5 Reaction to weather warnings

The following matrix identifies how Dorset Highways will strategically react to weather warnings or evidence of severe weather. For such events Dorset Highways and Dorset Council will partake in the Local Resilience Forum (LRF) Tactical Coordination Group (TCG) and Strategic Coordination Group (SCG) via teleconference. Acting as part of this will ensure a coordinated multiagency response is given to severe weather conditions.

Figure 1: Highways strategic response to severe weather conditions

Key: Green – No severe weather, Yellow – Low Impact, Amber – Widespread Disruption, Red – High Risk to Life

2. Flooding

2.1 Dorset has experienced a number of flood events over recent years and these fit under three headings, either fluvial, pluvial or tidal flooding. Working closely with the Environmental Agency and our internal Flood Risk Management team we have a good understanding of the impact of river levels on the county and the impact of intensive rain on surface water runoff.

2.2 Response to minor carriageway flooding will be through our standard business as usual operations reacting to in hours and out of hours call outs. This provides a 24-hour response to highway flooding issues.

2.3 For more severe weather warnings we will consider standing up a control room to strategically manage the response and work with the LRF if the TCG or SCG meet.

3.1 Dorset Council manages the impact of high winds on the highway and associated emergency responses. The extent of the service provided will vary depending upon the severity and nature of high wind conditions and resources availability. During normal working hours the response will be made by the Arboricultural team. Outside of working hours the response will be made by Dorset Highways

3.2 Dorset Council will have in house resources available and access to their supply chain to react to emergency situations.

3.3 Dorset Council has a tree policy Dorset Council online tree information which states the inspection period for the highway trees. These are the trees which DC are responsible for.

4.1 Dorset Highways monitors the weather throughout the year especially in times of prolonged periods of high temperatures when our carriageway surfacing could be affected as well as the delivery of our capital structural maintenance schemes.

4.2 Dorset Council’s Emergency Planning team has access to the Met Office to provide weather warnings in period of high temperatures as this has an impact on other services provided by the council. These weather warnings are circulated to Dorset Highways.

4.3 An extended period of elevated temperatures can have a detrimental effect on the highway network.

Carriageway melting

Bitumen within the surfacing material can begin to melt, this can in extreme circumstances result in a reduction of skid resistance. The micro texture of the material becomes saturated.

Remedial measures – Sites identified as becoming “soft” should be monitored throughout the period of elevated temperature. If the surface starts to appear “fatty” or polished the site should be dusted with 3mm to dust aggregate. This will restore skid resistance by both binding with the bitumen and aiding removal through abrasion. This process needs to be repeated until skid resistance is satisfactory.

Cracking due to shrinkage

Prolonged heat can cause rapid drying of subsoil leading to contraction, if the contraction is significant it can result in surface cracking and failure.

Remedial measures - Make safe and repair with safety defect procedure.