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

2 Background Quarmby Review and Report 2010 Recommended research to underpin initiatives for lower salt spread rates Recommended research to underpin initiatives for lower salt spread rates Research by TRL on behalf of the Highways Agency & National Winter Service Research Group Research by TRL on behalf of the Highways Agency & National Winter Service Research Group

3 TRL research was used to prepare a comprehensive range of recommended spread rates The recommended rates are based on: Weather conditions Weather conditions Gritter spreading capability Gritter spreading capability Road surface conditions Road surface conditions Salt Condition Salt Condition

4 Winter Service Guidance for Local Authority Practitioners The recommended salt spread rates have been incorporated into the ‘Well Maintained Highways’ The recommended salt spread rates have been incorporated into the ‘Well Maintained Highways’ This guidance is intended to provide users with confidence that the advice provided is sound from both a theoretical and practical point of view. This guidance is intended to provide users with confidence that the advice provided is sound from both a theoretical and practical point of view.

5 To comply with the guidance an assessment of the spreading capability is required prior to considering any treatment ‘Reasonable Capability ‘Reasonable Capability Salt must be in good condition i.e. moisture content between 2 and 3 %Salt must be in good condition i.e. moisture content between 2 and 3 % Gritters are new and have good technology spreadersGritters 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

6 Recommended Spread Rates For Pre-cautionary treatments ‘Reasonable’ Spreading Capability Frost or Forecast frost Dry Salting RST at or above -2 Degrees C and dry or damp road conditions 8 grms / sqm RST at or above –2 degrees C and wet road conditions 8 grms / sqm RST below –2 and above -5 degrees C and dry or damp road conditions 12 grms / sqm RST below –2 and above -5 degrees C and wet road conditions 20 grms / sqm

7 Recommended Spread Rates For Pre-cautionary treatments ‘Modest’ Spreading Capability Frost or Forecast frost Dry Salting RST at or above -2 Degrees C and dry or damp road conditions 8 grms / sqm RST at or above –2 degrees C and wet road conditions 11 grms / sqm RST below –2 and above -5 degrees C and dry or damp road conditions 15 grms / sqm RST below –2 and above -5 degrees C and wet road conditions 27 grms / sqm

8 What This Means  Local Authorities have the evidence of research to take confidence in the advice provided by NWSRG  However consideration has to be taken into what would be ideal conditions in research facilities against what most Local Authorities face on the ground.  In particular: Maintaining salt at between 2 and 3% MC Maintaining salt at between 2 and 3% MC Variance in the fleet operating from the same depot Variance in the fleet operating from the same depot The spread rates have been reduced at the lower end when marginal conditions are likely however the potential savings in salt at this lower spread rate are small in comparison to salt use in ‘severe weather’ The spread rates have been reduced at the lower end when marginal conditions are likely however the potential savings in salt at this lower spread rate are small in comparison to salt use in ‘severe weather’

9 REVIEWS  SCOTS Winter sub group The Group considered that the spreading at 8 grm/sqm will from a practical point be difficult to achieve. The Group considered that the spreading at 8 grm/sqm will from a practical point be difficult to achieve. The group is in agreement that a common spread rate for particular conditions is good practice but that it will always come back to local geographic and residual salt levels influencing decisions The group is in agreement that a common spread rate for particular conditions is good practice but that it will always come back to local geographic and residual salt levels influencing decisions

10 REVIEWS  Edinburgh, Lothians, Borders and Fife (ELBF) Shared Services Winter Group The group reviewed the guidance on salt spread rates and developed a common treatment matrix, taking into account the concerns over salt condition, gritter capabilities and practicalities The group reviewed the guidance on salt spread rates and developed a common treatment matrix, taking into account the concerns over salt condition, gritter capabilities and practicalities The matrix was derived using the following assumptions: The matrix was derived using the following assumptions:

11 Salt Condition  Due to salt storage limitations it is deemed that the local authorities will not be able to consistently achieve a ‘moisture’ level of 2 to 3% and as such all spread rates are based on ‘Modest’ spreading capability.

Carriageway Hierarchy (Before Snow or When Ice Formed)  The treatment guidance in the ‘Well Maintained Highways’ is based on two levels of road trafficking – heavily trafficked roads and medium / light trafficked roads.  The majority of roads within the Councils treatment routes are either main or secondary distributor, with any strategic routes likely to be incorporated in multiple road types. It has been determined that all treatments will be based on the criteria for medium / light traffic levels. It has been determined that all treatments will be based on the criteria for medium / light traffic levels.

Extract from the Agreed Common Treatment Matrix (Modest Capability) Frost or Forecast frost Dry Salting RST at or above -2 Degrees C and dry or damp road conditions 10 grms / sqm (Well Maintained Highways 8grms / sqm) RST at or above –2 degrees C and wet road conditions 10 grms / sqm (Well Maintained Highways 11grms / sqm) RST below –2 and above -5 degrees C and dry or damp road conditions 10 to 20grms / sqm (depending on residual salt) (Well Maintained Highways 15 grms) RST below –2 and above -5 degrees C and wet road conditions 20 grms / sqm (Well Maintained Highways 27grms) RST at or below –5 and above -10 degrees C and dry or damp road conditions 10 or 20 grms / sqm (depending on residual salt) (Well Maintained Highways 27grms) RST below –5 and above -10 degrees C and wet road conditions 20 grms / sqm (monitor for further treatments) (Well Maintained Highways 2 x 25grms)