Winter Service Plan 2008-9 (Abridged Version)
7.0 When do we act?
7.1 Arrangements have been made to receive “Open Road” weather forecasting service from the Met Office.
7.2 Pre-treatments should be carried out is indicated in Table H1 of the code of practice and shown below.
| Road Surface Temperature | Precipitation | Predicted Road Condition - Wet | Predicted Road Condition - Wet Patches | Predicted Road Condition - Dry |
|---|---|---|---|---|
| May fall below 1º C |
No rain, No hoar frost, No fog |
Salt before frost | Salt before frost (See note a) | No action likely, monitor weather (see note a) |
| Expected to fall below 1º C |
No rain, No hoar frost, No fog |
Salt before frost | Salt before frost (See note a) | No action likely, monitor weather (see note a) |
| Expected to fall below 1º C |
Expected hoar frost, Expected fog |
Salt before frost | Salt before frost (See note b) | Salt before frost (See note b) |
| Expected to fall below 1º C | Expected rain BEFORE freezing | Salt after rain stops (see note c) | Salt after rain stops (see note c) | Salt after rain stops (see note c) |
| Expected to fall below 1º C | Expected rain DURING freezing | Salt before frost, as required during rain and again after rain stops (see note d) | Salt before frost, as required during rain and again after rain stops (see note d) | Salt before frost, as required during rain and again after rain stops (see note d) |
| Expected to fall below 1º C | Possible rain, Possible hoar frost, Possible fog | Salt before frost | Salt before frost | Monitor weather conditions |
| Expected snow |
Salt before snow fall |
Salt before snow fall |
Salt before snow fall |
The decision to undertake precautionary treatments should, if appropriate, be justified to take account of residual salt or surface moisture. All decisions require continuous monitoring and review.
Notes:
a) Particular attention should be given to the possibility of water running across carriageways and other running surfaces eg, off adjacent fields after heavy rains, washing off salt previously deposited. Such locations should be closely monitored and may require treating in the evening and morning, and possible other occasions.
b) When a weather warning contains reference to expected hoarfrost considerable deposits of frost are likely to occur. Hoarfrost 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 hoarfrost 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 time of the condition. Hoarfrost may be forecast at other times in which case the timing of salting operations should be adjusted accordingly.
c) If, under these conditions, rain has not ceased by early morning, crews should be called out and action initiated as rain ceases.
d) Under these circumstances rain will freeze on contact with running surfaces and full pre–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 from each depot.
The table raises certain issues that must be interpreted in order to undertake treatments.
7.3 Road surface temperatures “may” fall below freezing. In practice the conditions whereby road surface temperatures of plus 2°C or plus 3°C are predicted are defined as “Marginal” conditions and actions planned accordingly. The first priority routes may be patrolled at the discretion of the Divisional Network Manager. The extent of this patrol may be varied according to conditions. If the patrol crews find significant areas of icy conditions they will inform the duty foreman and the Winter Operations Centre to initiate further action. Weather and information from ice sensors located in the road surface are monitored to enable plans to be adjusted accordingly. The above mechanism, associated with “Marginal” conditions will be continued until more sophisticated prediction is available.
7.4 Treat “before” the predicted adverse weather occurs. The code recommends that “the timing of operations should be mainly influenced by the timing of expected weather conditions rather than other considerations.” Ideally treatments carried out as close to the event as possible will be the most successful.
There are resourcing issues in providing operations during ‘out-of-working-hours’ times. At the discretion the Divisional Network Managers the extent of treatment during ‘out-of-working-hours’ times, may vary dependant upon the forecast conditions. If crews find significant areas of icy conditions they will inform the duty foreman and the Winter Operations Centre.
‘Out-of-working-hours’ will generally be defined as between the hours of 2000 – 0600 hrs.
Salt spread on a dry road may become dispersed by traffic or wind. Conversely salt spread on a wet road may be washed off by un-forecasted rainfall. In order to assist in determining whether it has rained at various parts of the road network 3 additional weather detectors were installed for the winter 2002/2003 and a further new site on the B6399 Berryfell will be installed this winter 2007/2008. (Residual salt i.e. salt remaining on the surface up to 24hours after treatment, is also difficult to measure and is currently the subject of research at the Transport Research Laboratory. – See also section 9.3)
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