1 SALT SPREAD RATES FOR PRECAUTIONARY AND POST TREATMENTS NWSRG Practical Guide for Winter Service.

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SALT SPREADSALT SPREAD RATES RATES FOR PRECAUTIONARY FOR PRECAUTIONARY

AND POST TREATMENTSAND POST TREATMENTS

NWSRG Practical Guide for NWSRG Practical Guide for Winter ServiceWinter Service

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BackgroundBackground

Quarmby Review and Report 2010Quarmby Review and Report 2010

Recommended research to underpin initiatives for lower Recommended research to underpin initiatives for lower salt spread ratessalt spread rates

Research by TRL on behalf of the Highways Agency & Research by TRL on behalf of the Highways Agency & National Winter Service Research GroupNational Winter Service Research Group

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TRL research was used to prepare a TRL research was used to prepare a comprehensive range of comprehensive range of

recommended spread ratesrecommended spread rates

The recommended rates are based on:The recommended rates are based on: Weather conditionsWeather conditions Gritter spreading capabilityGritter spreading capability Road surface conditionsRoad surface conditions Salt ConditionSalt Condition

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Winter Service Guidance for Local Winter Service Guidance for Local Authority PractitionersAuthority Practitioners

The recommended salt spread rates have The recommended salt spread rates have been incorporated into the ‘Well Maintained been incorporated into the ‘Well Maintained Highways’ Highways’

This guidance is intended to provide users This guidance is intended to provide users with confidence that the advice provided is with confidence that the advice provided is sound from both a theoretical and practical sound from both a theoretical and practical point of view.point of view.

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To comply with the guidance an assessment To comply with the guidance an assessment of the spreading capability is required prior of the spreading capability is required prior

to considering any treatmentto considering any treatment ‘‘Reasonable CapabilityReasonable Capability

• Salt must be in good condition i.e. moisture content Salt must be in good condition i.e. moisture content between 2 and 3 %between 2 and 3 %

• Gritters are new and have good technology spreaders Gritters are new and have good technology spreaders ‘‘Modest Capability’Modest Capability’

• Gritters are old or relatively low technology spreadersGritters are old or relatively low technology spreaders

• Salt has been stored in less than optimal conditionsSalt has been stored in less than optimal conditions

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Recommended Spread Rates Recommended Spread Rates

For Pre-cautionary treatments For Pre-cautionary treatments

‘‘Reasonable’Reasonable’ Spreading Capability Spreading Capability

Frost or Forecast frostFrost or Forecast frost Dry SaltingDry Salting

RST at or above -2 Degrees C and RST at or above -2 Degrees C and dry or damp road conditionsdry or damp road conditions

8 grms / sqm8 grms / sqm

RST at or above –2 degrees C and RST at or above –2 degrees C and wet road conditionswet road conditions


RST below –2 and above -5 degrees RST below –2 and above -5 degrees C and dry or damp road conditionsC and dry or damp road conditions


RST below –2 and above -5 degrees RST below –2 and above -5 degrees C and wet road conditionsC and wet road conditions


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Recommended Spread Rates Recommended Spread Rates

For Pre-cautionary treatments For Pre-cautionary treatments

‘‘Modest’Modest’ Spreading Capability Spreading Capability


RST at or above -2 Degrees C and dry or damp RST at or above -2 Degrees C and dry or damp road conditionsroad conditions


RST at or above –2 degrees C and wet road RST at or above –2 degrees C and wet road conditionsconditions


RST below –2 and above -5 degrees C and dry RST below –2 and above -5 degrees C and dry or damp road conditionsor damp road conditions


RST below –2 and above -5 degrees C and wet RST below –2 and above -5 degrees C and wet road conditionsroad conditions


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What This MeansWhat This Means Local Authorities have the evidence of research Local Authorities have the evidence of research

to take confidence in the advice provided by to take confidence in the advice provided by NWSRGNWSRG

However consideration has to be taken into what However consideration has to be taken into what would be ideal conditions in research facilities would be ideal conditions in research facilities against what most Local Authorities face on the against what most Local Authorities face on the ground.ground.

In particular:In particular: Maintaining salt at between 2 and 3% MCMaintaining salt at between 2 and 3% MC Variance in the fleet operating from the same depotVariance in the fleet operating from the same depot The spread rates have been reduced at the lower end when marginal The spread rates have been reduced at the lower end when marginal

conditions are likely however the potential savings in salt at this lower conditions are likely however the potential savings in salt at this lower spread rate are small in comparison to salt use in ‘severe weather’ spread rate are small in comparison to salt use in ‘severe weather’

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REVIEWSREVIEWS

SCOTS Winter sub groupSCOTS Winter sub group The Group considered that the spreading at 8 The Group considered that the spreading at 8

grm/sqm will from a practical point be difficult to grm/sqm will from a practical point be difficult to achieve.achieve.

The group is in agreement that a common spread rate The group is in agreement that a common spread rate for particular conditions is good practice but that it will for particular conditions is good practice but that it will always come back to local geographic and residual always come back to local geographic and residual salt levels influencing decisionssalt levels influencing decisions

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REVIEWSREVIEWS

Edinburgh, Lothians, Borders and Fife Edinburgh, Lothians, Borders and Fife (ELBF) Shared Services Winter Group(ELBF) Shared Services Winter Group The group reviewed the guidance on salt The group reviewed the guidance on salt

spread rates and developed a common spread rates and developed a common treatment matrix, taking into account the treatment matrix, taking into account the concerns over salt condition, gritter concerns over salt condition, gritter capabilities and practicalitiescapabilities and practicalities

The matrix was derived using the following The matrix was derived using the following assumptions:assumptions:

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Salt ConditionSalt Condition Due to salt storage limitations it is Due to salt storage limitations it is

deemed that the local authorities will deemed that the local authorities will not be able to consistently achieve a not be able to consistently achieve a ‘moisture’ level of 2 to 3% and ‘moisture’ level of 2 to 3% and as such as such all spread rates are based on ‘Modest’ all spread rates are based on ‘Modest’ spreading capability.spreading capability.

Carriageway HierarchyCarriageway Hierarchy(Before Snow or When Ice Formed)(Before Snow or When Ice Formed)

The treatment guidance in the ‘Well Maintained The treatment guidance in the ‘Well Maintained Highways’ is based on two levels of road trafficking – Highways’ is based on two levels of road trafficking – heavily trafficked roads and medium / light trafficked heavily trafficked roads and medium / light trafficked roads.roads.

The majority of roads within the Councils treatment The majority of roads within the Councils treatment routes are either main or secondary distributor, with routes are either main or secondary distributor, with any strategic routes likely to be incorporated in multiple any strategic routes likely to be incorporated in multiple road types.road types. It has been determined that all It has been determined that all

treatments will be based on the criteria treatments will be based on the criteria for medium / light traffic levels.for medium / light traffic levels.

Extract from the Agreed Common Treatment Matrix Extract from the Agreed Common Treatment Matrix (Modest Capability)(Modest Capability)


RST at or above -2 Degrees C and dry or damp RST at or above -2 Degrees C and dry or damp road conditionsroad conditions


(Well Maintained Highways 8grms / sqm)(Well Maintained Highways 8grms / sqm)

RST at or above –2 degrees C and wet road RST at or above –2 degrees C and wet road conditionsconditions


(Well Maintained Highways 11grms / sqm)(Well Maintained Highways 11grms / sqm)

RST below –2 and above -5 degrees C and dry or RST below –2 and above -5 degrees C and dry or damp road conditionsdamp road conditions

10 to 20grms / sqm10 to 20grms / sqm

(depending on residual salt)(depending on residual salt)

(Well Maintained Highways 15 grms)(Well Maintained Highways 15 grms)



(Well Maintained Highways 27grms)(Well Maintained Highways 27grms)

RST at or below –5 and above -10 degrees C and RST at or below –5 and above -10 degrees C and dry or damp road conditionsdry or damp road conditions

10 or 20 grms / sqm10 or 20 grms / sqm

(depending on residual salt)(depending on residual salt)

(Well Maintained Highways 27grms)(Well Maintained Highways 27grms)



(monitor for further treatments)(monitor for further treatments)

(Well Maintained Highways 2 x 25grms)(Well Maintained Highways 2 x 25grms)

1 SALT SPREAD RATES FOR PRECAUTIONARY AND POST TREATMENTS NWSRG Practical Guide for Winter Service.

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